The brain of any computer system is

ANS:C - CPU

CPU= Central Processing Unit.

It's a Microprocessor (It's a chip). It contains millions of transistors which help in manipulate data. There's an ALU (arithmetic-logic unit) part which performs calculation within seconds. Also, CU (Control Unit) gives the result of execution (as taking input and instruction from a program it respond for output).

Further, the ALU is divided into two units, an arithmetic unit (AU) and a logic unit (LU). You may say a CPU as the decision maker.

In simple language, Fetching Instruction from Main Memory to CU, then decoding instruction into command, ALU help to execute the program and again it stores in the memory. A complete cycle goes on.