When you are building a C program out of many C source files, which of the

following are true?

A: You can't call functions in other C files unless they were defined in a

common header file.

B: You can have only a single main function, and if you try to have more

than one, this is an error.

C: You can define which main function you want to call as a compile$-$time

option, specified in your Makefile.

D: Each C file can have its own main function as long as they have

distinct return values.