Central Processing Unit (CPU): It is the most important unit, where all the processing jobs take place. CPU is the control centre of the computer and hence it is said to be the brain of the computer. CPU has three main components:

1. Arithmetic Logic Unit (ALU): It performs all the arithmetic operations like addition (+), multiplication (*), subtraction (-), division (/) on the numerical data directed by the control unit. All the logical operations, like less than (<), greater="" than="" (="">), equal to (ALU also carries out =), not equal to (≠) etc..
2. Control Unit (CU): It controls and coordinates all the operations taking place in the system. It controls the flow of data and information from one unit to the other.
3. Registers/Memory Unit (MU): To execute a program, data and instructions need to be stored temporarily. This storage is done in the MU. The data and instructions are retrieved from MU by Control Unit to supply ALU as required by the program.
   

Central Processing Unit (CPU): It is the most important unit, where all the processing jobs take place. CPU is the control centre of the computer and hence it is said to be the brain of the computer. CPU has three main components:

1. Arithmetic Logic Unit (ALU): It performs all the arithmetic operations like addition (+), multiplication (*), subtraction (-), division (/) on the numerical data directed by the control unit. All the logical operations, like less than (<), greater="" than="" (="">), equal to (ALU also carries out =), not equal to (≠) etc..
2. Control Unit (CU): It controls and coordinates all the operations taking place in the system. It controls the flow of data and information from one unit to the other.
3. Registers/Memory Unit (MU): To execute a program, data and instructions need to be stored temporarily. This storage is done in the MU. The data and instructions are retrieved from MU by Control Unit to supply ALU as required by the program.
   

Explanation:

The correct answer is option 'B' - Central Processing Unit (CPU).

Definition:
- The Central Processing Unit (CPU) is the primary component of a computer system that performs most of the processing inside the computer.
- It is often referred to as the "brain" of the computer because it carries out the instructions of a computer program by performing basic arithmetic, logical, control, and input/output (I/O) operations.

Functions of CPU:
1. Arithmetic and Logic Unit (ALU):
- The ALU is responsible for performing arithmetic and logical operations, such as addition, subtraction, multiplication, division, and comparisons.
- It performs these operations on data stored in the computer's memory or registers.

2. Control Unit (CU):
- The Control Unit manages and coordinates the activities of the CPU.
- It fetches instructions from memory, decodes them, and then executes them by directing the ALU and other components to perform the necessary operations.
- It also controls the flow of data between the CPU, memory, and input/output devices.

3. Registers:
- The CPU contains various registers that store data and instructions temporarily during processing.
- These registers include the program counter (PC), which keeps track of the next instruction to be executed, and the instruction register (IR), which holds the current instruction being executed.

4. Cache:
- The CPU also has a cache, which is a small, fast memory used to store frequently accessed data and instructions.
- The cache helps to improve the overall performance of the CPU by reducing the time it takes to access data from the main memory.

Conclusion:
In summary, the CPU (Central Processing Unit) is the main component of a computer system responsible for executing instructions, performing arithmetic and logical operations, and managing the flow of data. It is often considered the "brain" of the computer and is essential for the functioning of any digital device.