Functions can: A. Be used as building blocks to create new programs. B. Return a result to the caller function. C. Be reused any number of times. D. Do all of the above.

D. Do all of the above.

Explanation:

Function: In computer science, the term "function" is described as a process in which it executes, then returns a specific value, and lastly resumes a particular program where the function has been called or initiated. Thus, in the "programming system," a specific named section associated with a program is present that is responsible for performing some specified tasks and is denoted as a "function". In other words, the function is referred to as a kind of routine or procedure.

In the question above, the correct answer is option-D.