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Syllabus

NEC Computer · Practice

Chapters & sets

1. Basic Electrical and Electronics

Basic Electrical

Set 1106

Basic Electronics

Set 171 Set 233

2. Digital Logic and Microprocessor

Digital Logic

Set 150 Set 250 Set 350 Set 450 Set 550 Set 650 Set 749 Set 851 Set 950 Set 1050 Set 1150 Set 1232

Microprocessor

Set 150 Set 250 Set 350 Set 445 Set 550 Set 650 Set 720 Set 850 Set 969

3. Programming Language and Its Applications

Mixed chapter MCQs

Set 150 Set 249 Set 349 Set 451 Set 540

4. Computer Organization and Embedded System

Mixed chapter MCQs

Set 150 Set 249 Set 350 Set 450 Set 550 Set 650 Set 750 Set 849 Set 950 Set 1050 Set 1150

5. Concept of Computer Network and Network Security System

Basic Networking

Set 150 Set 253

Advanced Networking

Set 150 Set 250 Set 350 Set 450 Set 550 Set 655

6. Theory of Computation and Computer Graphics

Theory of Computation

Set 150 Set 250 Set 360

Computer Graphics

Set 150 Set 251 Set 350 Set 450 Set 550

7. Data Structures and Algorithm, Database System and Operating System

8. Software Engineering and Object-Oriented Analysis & Design

Mixed chapter MCQs

Set 150 Set 250 Set 350 Set 450 Set 550 Set 650 Set 750 Set 926

9. Artificial Intelligence and Neural Networks

Mixed chapter MCQs

Set 150 Set 317 Set 450 Set 550 Set 650 Set 750 Set 850 Set 932

10. Project Planning, Design and Implementation

Engineering Drawing

Set 150 Set 267

Engineering Economics

Set 168

Project Planning & Scheduling

Set 188

Project Mangement

Set 150

Engineering Professional Practice

Set 120

Engineering Regulatory Body

Set 130

Basic Electrical Set 1

106 questions

Question 1

Energy per unit charge is ____________

A.
Power
B.
Voltage
C.
Current
D.
Capacitance

Question 2

A conductor is said to have resistance of one ohm if a potential difference of one volt across its terminals causes a current of X ampere to flow through it. What will be the value of X?

50

A.
4
B.
2
C.
3
D.
1

Question 3

Resistance depends on the temperature of the conductor.

A.
True
B.
False

Question 4

A 25 Ω resistor has a voltage of 150 sin(377 t). Find the corresponding power.

A.
$900 \sin^2(337 t)$
B.
$90 \sin^2(337 t)$
C.
$900 \sin^2(377 t)$
D.
$9 \sin^2(337 t)$

Question 5

Unit of inductance is ________

A.
Weber
B.
Henry
C.
Farad
D.
Tesla

Question 6

Inductance of an inductor is inversely proportional to its ___________

A.
Number of turns
B.
Area of cross section
C.
Absolute permeability
D.
Length

Question 7

Energy stored in an inductor is ________

A.
$L I$
B.
$L I^2$
C.
$\frac{L I}{2}$
D.
$\frac{L I^2}{2}$

Question 8

An inductor of 3 mH has a current

i = 5(1 - e^{-5000t})

. Find the corresponding maximum energy stored.

A.
37.5 mJ
B.
375 J
C.
37.5 kJ
D.
3.75 mJ

Question 9

The capacitance of a capacitor does not depend on the absolute permittivity of the medium between the plates.

A.
True
B.
False

Question 10

Which of the following is not the energy stored in a capacitor?

A.
$\frac{C V^2}{2}$
B.
$\frac{Q V}{2}$
C.
$\frac{Q^2}{2 C}$
D.
$\frac{Q C}{2}$

Question 11

A voltage is defined by:

v(t) = \begin{cases} 0 & \text{for } t < 0 \ 2t & \text{for } 0 < t < 2 \text{ s} \ 4 e^{-(t-2)} & \text{for } t > 2 \text{ s} \end{cases}

and is applied to the 10 µF capacitor. Which of the following is incorrect?

A.
$i = 0$ for $t < 0$
B.
$i = 20 \ \mu \text{A}$

Question 12

Source is a basic network element which supplies power to the networks.

A.
True
B.
False

Question 13

The dependent sources are of _____________ kinds.

A.
5
B.
2
C.
3
D.
4

Question 14

The constant gm has dimension of ___________

A.
Ampere per volt
B.
Ampere
C.
Volt
D.
Volt per ampere

Question 15

In CCVS, voltage depends on the control current and the constant called __________

A.
Transconductance
B.
Transresistance
C.
Current Gain
D.
Voltage Gain

Question 16

Every circuit is a network, but all networks are not circuits.

A.
True
B.
False

Question 17

Which of the following is not an example of a linear element?

A.
Resistor
B.
Thermistor
C.
Inductor
D.
Capacitor

Question 18

Find the odd one out.

A.
Resistor
B.
Voltage-dependent resistor(VDR)
C.
Temperature-dependent resistor(Thermistor)
D.
Light-dependent resistor(LDR)

Question 19

Which of the following is an Active element?

A.
Resistor
B.
Inductor
C.
Capacitor
D.
OP-AMP

Question 20

A semiconductor diode is an ____________ element.

A.
Bilateral
B.
Unilateral
C.
Active
D.
Passive

Question 21

Example of distributed element is ___________

A.
Resistor
B.
Thermistor
C.
Semiconductor diode
D.
Transmission lines

Question 22

Potential difference in electrical terminology is known as?

A.
Voltage
B.
Current
C.
Resistance
D.
Conductance

Question 23

The circuit in which current has a complete path to flow is called ______ circuit.

A.
short
B.
open
C.
closed
D.
open loop

Question 24

If the voltage-current characteristics is a straight line through the origin, then the element is said to be?

A.
Linear element
B.
Non-linear element
C.
Unilateral element
D.
Bilateral element

Question 25

The voltage across R1 resistor in the circuit shown below is? *(Assume a circuit with a 10V source and two equal resistors R1 and R2 in series.)* Circuit diagram from the source question

Circuit diagram from the source question

A.
10
B.
5
C.
2.5
D.
1.25

Question 26

The energy stored in the inductor is?

A.
$\frac{L i^2}{4}$
B.
$\frac{L i^2}{2}$
C.
$L i^2$
D.
$\frac{L i^2}{8}$

Question 27

How many types of dependent or controlled sources are there?

A.
1
B.
2
C.
3
D.
4

Question 28

Find the voltage Vx in the given circuit. *(Assume a single loop with a 50V source, and voltage drops of 15V, 10V, 15V across three elements, with Vx as the remaining drop.)* Circuit diagram from the source question

A.
10
B.
20
C.
30
D.
40

Question 29

If the resistances 1Ω, 2Ω, 3Ω, 4Ω are parallel, then the equivalent resistance is?

A.
0.46Ω
B.
0.48Ω
C.
0.50Ω
D.
0.52Ω

Question 30

Find total current(mA) in the circuit. *(Assume a circuit with a 3V source and a total equivalent resistance of 3 kΩ.)* Circuit diagram from the source question

A.
1
B.
2
C.
3
D.
4

Question 31

If the resistances 3Ω, 5Ω, 7Ω, 9Ω are in series, then their equivalent resistance(Ω) is?

A.
9
B.
20
C.
24
D.
32

Question 32

Pick the incorrect statement among the following.

A.
Inductor is a passive element
B.
Current source is an active element
C.
Resistor is a passive element
D.
Voltage source is a passive element

Question 33

For a voltage source to be neglected, the terminals across the source should be ___________

A.
replaced by inductor
B.
short circuited
C.
replaced by some resistance
D.
open circuited

Question 34

Voltage source and terminal voltage can be related as ___________

A.
terminal voltage is higher than the source emf
B.
terminal voltage is equal to the source emf
C.
terminal voltage is always lower than source emf
D.
terminal voltage cannot exceed source emf

Question 35

In case of ideal current sources, they have ___________

A.
zero internal resistance
B.
low value of voltage
C.
large value of current
D.
infinite internal resistance

Question 36

In a network consisting of linear resistors and ideal voltage source, if the value of resistors are doubled, then voltage across each resistor ___________

A.
increases four times
B.
remains unchanged
C.
doubled
D.
halved

Question 37

A practical current source can also be represented as ___________

A.
a resistance in parallel with an ideal voltage source
B.
a resistance in parallel with an ideal current source
C.
a resistance in series with an ideal current source
D.
none of the mentioned

Question 38

A practical voltage source can also be represented as ___________

A.
a resistance in series with an ideal current source
B.
a resistance in series with an ideal voltage source
C.
a resistance in parallel with an ideal voltage source
D.
none of the mentioned

Question 39

Constant voltage source is ___________

A.
active and bilateral
B.
passive and bilateral
C.
active and unilateral
D.
passive and unilateral

Question 40

Which of the following is true about an ideal voltage source?

A.
zero resistance
B.
small emf
C.
large emf
D.
infinite resistance

Question 41

A dependent source ___________

A.
may be a current source or a voltage source
B.
is always a voltage source
C.
is always a current source
D.
none of the mentioned

Question 42

With some initial change at t = 0+, a capacitor will act as ___________

A.
open circuit
B.
short circuit
C.
a current source
D.
a voltage source

Question 43

If a current source is to be neglected, the terminals across the source are ___________

A.
replaced by a source resistance
B.
open circuited
C.
replaced by a capacitor
D.
short circuited

Question 44

A constant current source supplies a electric current of 200 mA to a load of 2kΩ. When the load changed to 100Ω, the load current will be ___________

A.
9mA
B.
4A
C.
700mA
D.
12A

Question 45

A voltage source having an open circuit voltage of 200 V and internal resistance of 50Ω is equivalent to a current source of ___________

A.
4A with 50Ω in parallel
B.
4A with 50Ω in series
C.
0.5A with 50Ω in parallel
D.
none of the mentioned

Question 46

A voltage source of 300 V has internal resistance of 4Ω and supplies a load having the same resistance. The power absorbed by the load is?

A.
1150 W
B.
1250 W
C.
5625 W
D.
5000 W

Question 47

Resistance of a wire is yΩ. The wire is stretched to triple its length, then the resistance becomes ___________

A.
y/3
B.
3y
C.
6y
D.
y/6

Question 48

An electric current of 10 A is the same as ___________

A.
10 J/C
B.
10 V/C
C.
10 C/sec
D.
10 W/sec

Question 49

Consider a circuit with two unequal resistances in parallel, then ___________

A.
large current flows in large resistor
B.
current is same in both
C.
potential difference across each is same
D.
smaller resistance has smaller conductance

Question 50

In which of the following cases is Ohm’s law not applicable?

A.
Electrolytes
B.
Arc lamps
C.
Insulators
D.
Vacuum ratio values

Question 51

A copper wire of length l and diameter d has potential difference V applied at its two ends. The drift velocity is V. If the diameter of wire is made d/4, then drift velocity becomes ___________

A.
V/16
B.
16V
C.
V
D.
V/4

Question 52

Which of the following bulbs will have high resistance?

A.
220V, 60W
B.
220V, 100W
C.
115V, 60W
D.
115V, 100W

Question 53

Ohm’s law is not applicable to ___________

A.
dc circuits
B.
high currents
C.
small resistors
D.
semi-conductors

Question 54

Conductance is expressed in terms of ___________

A.
mho
B.
mho/m
C.
ohm/m
D.
m/ohm

Question 55

Resistivity of a wire depends on ___________

A.
length of wire
B.
cross section area
C.
material
D.
all of the mentioned

Question 56

In a current-voltage relationship graph of a linear resistor, the slope of the graph will indicate ___________

A.
conductance
B.
resistance
C.
resistivity
D.
a constant

Question 57

Kirchhoff’s Current law is based on the law of conservation of ___________

A.
energy
B.
momentum
C.
mass
D.
charge

Question 58

The current law represents a mathematical statement of fact that ___________

A.
voltage cannot accumulate at node
B.
charge cannot accumulate at node
C.
charge at the node is infinite
D.
none of the mentioned

Question 59

Kirchhoff’s current law is applied at ___________

A.
loops
B.
nodes
C.
both loop and node
D.
none of the mentioned

Question 60

Determine the current in all resistors in the circuit shown below. *(Assume a circuit with a 50A current source and three resistors in parallel: 7Ω, 3Ω, 5Ω.)* Circuit diagram from the source question

A.
2A, 4A, 11A
B.
5A, 4.8A, 9.6A
C.
9.3A, 20.22A, 11A
D.
10.56A, 24.65A, 14.79A

Question 61

For the circuit below , find the voltage across 5Ω resistor and the current through it. *(Assume a circuit with a 10A current source entering a node, with parallel branches: 15Ω, 5Ω, 2Ω, 1Ω, and a 5A current source leaving the node.)* Circuit diagram from the source question

A.
1.93 V
B.
2.83 V
C.
3.5 V
D.
5.7 V

Question 62

Determine the current through the resistor R3 shown in the figure using KCL. *(Assume a node with entering currents: 60mA; leaving currents: 10mA through R1, 25mA through R2, and unknown i3 through R3.)* Circuit diagram from the source question

A.
25mA
B.
10mA
C.
20mA
D.
35mA

Question 63

Find the current i3 in the circuit shown below. *(Assume a node with entering current 5A and leaving currents: 2A and i3.)* Circuit diagram from the source question

A.
2A
B.
1A
C.
3A
D.
0.5A

Question 64

Kirchhof’s current law can be mathematically stated as ___________

A.
$\sum_{k=0}^{n} I = 0$
B.
$i^2 \sum_{k=0}^{n} I = 0$
C.
$i \sum_{k=0}^{n} I = 0$
D.
none of the mentioned

Question 65

Determine the current if a 20 coulomb charge passes a point in 0.25 seconds.

A.
10 A
B.
20 A
C.
2 A
D.
80 A

Question 66

Find the current through the branch containing resistance R3. *(Assume a node with entering current 5A and leaving currents: 0.25A, 2A, and unknown i3 through R3.)* Circuit diagram from the source question

A.
2A
B.
3.25A
C.
2A
D.
2.75A

Question 67

Kirchhoff’s Voltage Law is based on the law of conservation of ___________

A.
energy
B.
momentum
C.
mass
D.
charge

Question 68

Kirchhoff’s voltage law is concerned with ___________

A.
IR drops
B.
battery emf
C.
junction voltages
D.
both (1) and (2)

Question 69

Kirchhoff’s voltage law is applied at ___________

A.
loops
B.
nodes
C.
both loop and node
D.
none of the mentioned

Question 70

In the circuit below, find the value of

V_x

using KVL. *(Assume a single loop with a 12V battery, a 2Ω resistor with voltage drop V1, and a dependent source Vx = 2\*I.)* Circuit diagram from the source question

A.
4V
B.
8V
C.
12V
D.
6V

Question 71

For the circuit below, determine the voltage

V_1

using KVL. Circuit diagram from the source question

*(Assume two loops: Left loop with 20V source, 5Ω resistor (V1), and shared 10Ω resistor. Right loop with shared 10Ω resistor, 4Ω resistor, and 10V source.)*

A.
5V
B.
10V
C.
15V
D.
20V

Question 72

Determine the unknown voltage

V

in the circuit below using KVL. Circuit diagram from the source question

*(Assume a single loop: 50V source, 10Ω resistor with 20V drop, 15Ω resistor with 30V drop, and unknown voltage source V with polarity opposing the loop direction.)*

A.
10V
B.
0V
C.
50V
D.
100V

Question 73

Find the current

I

in the circuit using KVL. Circuit diagram from the source question

*(Assume a single loop with voltage sources: 12V, 5V, and 3V; and resistors: 2Ω and 4Ω.)*

A.
1A
B.
2A
C.
3A
D.
4A

Question 74

Kirchhoff’s voltage law can be mathematically stated as ___________

A.
$\sum_{k=1}^{n} V_k = 0$
B.
$V^2 \sum_{k=1}^{n} V_k = 0$
C.
$V \sum_{k=1}^{n} V_k = 0$
D.
none of the mentioned

Question 75

In a closed loop, the algebraic sum of the potential differences across each circuit element is equal to ___________

A.
the sum of the emfs in the loop
B.
zero
C.
the product of the emfs in the loop
D.
the sum of the resistances in the loop

Question 76

Determine the voltage

V_{ab}

in the circuit below using KVL. Circuit diagram from the source question

*(Assume two loops sharing a 5Ω resistor. Left loop: 10V source, 2Ω resistor, shared 5Ω. Right loop: shared 5Ω, 3Ω resistor, 5V source.)*

A.
2V
B.
5V
C.
7V
D.
10V

Question 77

Mesh analysis is applicable for non planar networks also.

A.
true
B.
false

Question 78

A mesh is a loop which contains ______ number of loops within it.

A.
1
B.
2
C.
3
D.
no loop

Question 79

Consider the circuit shown below. The number of mesh equations that can be formed is? *(Assume a circuit with two obvious inner loops/meshes.)* Circuit diagram from the source question

A.
1
B.
2
C.
3
D.
4

Question 80

In the figure shown below, the current through loop 1 is I₁ and through loop 2 is I₂. Then the current flowing through the resistor R₂ will be? *(Assume two meshes sharing a common resistor R₂. Loop 1 current I₁ is clockwise, Loop 2 current I₂ is clockwise.)* Circuit diagram from the source question

A.
I₁
B.
I₂
C.
I₁ - I₂
D.
I₁ + I₂

Question 81

If there are 5 branches and 4 nodes in a graph, then the number of mesh equations that can be formed is?

A.
2
B.
4
C.
6
D.
8

Question 82

Consider the circuit shown in the figure. Find voltage Vₓ. *(Assume a circuit with two meshes. Mesh 1: 5V source and 2Ω resistor. Mesh 2: 4Ω resistor with Vₓ across it. A dependent source relates the two meshes.)* Circuit diagram from the source question

A.
1
B.
1.25
C.
1.5
D.
1.75

Question 83

Consider the circuit shown below. Find the current I₁ (A). *(Assume a circuit with three meshes. Resistors: 1Ω, 3Ω, 6Ω in one mesh; 2Ω, 5Ω, 3Ω in second; a 10Ω in third. Sources: 10V, 4V, 20V, 4V in various branches.)* Circuit diagram from the source question

A.
3.32
B.
3.78
C.
5.33
D.
6.38

Question 84

Consider the following figure. Find the current I₂ (A). Circuit diagram from the source question

A.
1.5
B.
2.6
C.
3.6
D.
4.6

Question 85

Consider the following figure. Find the current I₃ (A). Circuit diagram from the source question

A.
4.34
B.
3.86
C.
5.45
D.
5.72

Question 86

Find current through R₂ resistor. Circuit diagram from the source question

*(Assume a circuit with two meshes. Left mesh: 10V source, 5Ω resistor (R₁?), and 2Ω resistor (R₂) shared. Right mesh: 40V source, 10Ω resistor, and shared 2Ω resistor.)*

A.
3
B.
3.25
C.
3.5
D.
3.75

Question 87

If there are 8 nodes in a network, we can get ____ number of equations in nodal analysis.

A.
9
B.
8
C.
7
D.
6

Question 88

Nodal analysis can be applied for non-planar networks also.

A.
true
B.
false

Question 89

In nodal analysis, how many nodes are taken as reference nodes?

A.
1
B.
2
C.
3
D.
4

Question 90

Find the voltage at node P in the following figure. Circuit diagram from the source question

*(Assume node P connected via 2Ω resistor to a 4V source, via 3Ω resistor to a -6V source, and with a 3A current source entering node P.)*

A.
8V
B.
9V
C.
10V
D.
11V

Question 91

Find the resistor value R₁ (Ω) in the figure shown below. Circuit diagram from the source question

*(Assume a circuit with three nodes: V₁=100V, V₂=30V, V₃=40V. A 10A current enters node V₁, which connects to V₂ via 14Ω and to V₃ via R₁.)*

A.
10
B.
11
C.
12
D.
13

Question 92

Find the value of the resistor R₂ (Ω) in the circuit shown below. Circuit diagram from the source question

A.
5
B.
6
C.
7
D.
8

Question 93

Find the voltage (V) at node 1 in the circuit shown. *(Assume a circuit with two non-reference nodes. Node 1 connected to: 10A current source, 1Ω, 2Ω, 3Ω resistors. Node 2 connected to: 2A and 5A sources, 3Ω, 6Ω, 5Ω resistors.)* Circuit diagram from the source question

A.
5.32
B.
6.32
C.
7.32
D.
8.32

Question 94

Find the voltage (V) at node 2 in the circuit shown below. Circuit diagram from the source question

A.
2.7
B.
3.7
C.
4.7
D.
5.7

Question 95

Find the voltage at node 1 of the circuit shown below. *(Assume two nodes. Node 1: connected to 10A source, 10Ω resistor to ground, and 3Ω resistor to node 2. Node 2: connected to 10V source, 5Ω resistor to ground, 1Ω resistor to ground, and 3Ω resistor to node 1.)* Circuit diagram from the source question

A.
32.7
B.
33.7
C.
34.7
D.
35.7

Question 96

Find the voltage at node 2 of the circuit shown below. Circuit diagram from the source question

A.
13
B.
14
C.
15
D.
16

Question 97

If resistors

R_x

,

R_y

,

R_z

are connected between nodes X-Y, X-Z, Y-Z to form a delta, then after transformation to star, the resistor at node X is:

A.
$\frac{R_x R_y}{R_x + R_y + R_z}$

Question 98

If resistors

R_x

,

R_y

,

R_z

are connected between nodes X-Y, X-Z, Y-Z to form a delta, then after transformation to star, the resistance at node Y is:

A.
$\frac{R_z R_y}{R_x + R_y + R_z}$

Question 99

If resistors

R_x

,

R_y

,

R_z

are connected between nodes X-Y, X-Z, Y-Z to form a delta, then after transformation to star, the resistance at node Z is:

A.
$\frac{R_y R_x}{R_x + R_y + R_z}$

Question 100

If the resistors of a star-connected system are

R_1

,

R_2

,

R_3

, then the resistance between nodes 1 and 2 in the equivalent delta-connected system will be:

A.
$\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_3}$

Question 101

If the resistors of a star-connected system are

R_1

,

R_2

,

R_3

, then the resistance between nodes 2 and 3 in the equivalent delta-connected system will be:

A.
$\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_3}$

Question 102

If the resistors of a star-connected system are

R_1

,

R_2

,

R_3

, then the resistance between nodes 3 and 1 in the equivalent delta-connected system will be:

A.
$\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_1}$

Question 103

Find the equivalent resistance at node A in the delta-connected circuit shown below. Circuit diagram from the source question

A.
1
B.
2
C.
3
D.
3.67

Question 104

Find the equivalent resistance at node C in the delta-connected circuit shown below. Circuit diagram from the source question

A.
3.66
B.
4.33
C.
5.66
D.
6.66

Question 105

Find the equivalent resistance between node 1 and node 3 in the star-connected circuit shown below. Circuit diagram from the source question

*(Assume star with:*

R_1 = 10\Omega

*,*

R_2 = 10\Omega

*,*

R_3 = 11\Omega

*.)*

A.
30
B.
31
C.
32
D.
33

Question 106

Find the equivalent resistance between node 1 and node 2 in the star-connected circuit shown below. Circuit diagram from the source question

*(Same star:*

R_1 = 10\Omega

*,*

R_2 = 10\Omega

*,*

R_3 = 11\Omega

*.)*

A.
2
B.
29
C.
30
D.
31

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for

0 < t < 2 \text{ s}

C.

i = 40 e^{t-2} \ \mu \text{A}

for

t > 2 \text{ s}

D.

i = -40 e^{-(t-2)} \ \mu \text{A}

for

t > 2 \text{ s}

B.

\frac{R_x R_z}{R_x + R_y + R_z}

C.

\frac{R_z R_y}{R_x + R_y + R_z}

D.

\frac{R_x + R_y}{R_x + R_y + R_z}

B.

\frac{R_z R_x}{R_x + R_y + R_z}

C.

\frac{R_x R_y}{R_x + R_y + R_z}

D.

\frac{R_z + R_y}{R_x + R_y + R_z}

B.

\frac{R_y R_x}{R_x + R_y + R_z}

C.

\frac{R_z R_y}{R_x + R_y + R_z}

D.

\frac{R_z + R_x}{R_x + R_y + R_z}

B.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_1}

C.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_2}

D.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_1 + R_2}

B.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_2}

C.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_1}

D.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_3 + R_2}

B.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_3}

C.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_2}

D.

\frac{R_1 R_2 + R_2 R_3 + R_3 R_1}{R_3 + R_1}