A computer consists of

The correct answer is D: All of these
Let's break down why:
Option A: A central processing unit (CPU) is like the "brain" of the computer. It performs calculations and controls all other parts.
Option B: A memory is where the computer stores information and instructions it needs to use quickly. Think of it as short-term storage.
Option C: Input and output unit are how the computer interacts with you and the outside world. Input devices (like a keyboard or mouse) let you send information to the computer, and output devices (like a monitor or printer) let the computer show you the results.
Since a computer needs all three of these (a brain, a memory, and a way to interact), the answer is all of these.