Which header file should be included for input and output functions in C?

The header file that should be included for input and output functions in C is Option B: <stdio.h>. The <stdio.h> header file provides declarations for functions like printf, scanf, getchar, and many others that are used for input and output operations in C.

So, the correct answer is:

Option B: <stdio.h>

Including this header file at the beginning of your C program allows you to use standard input and output functions to interact with the user and manipulate data.