This is a question of C-programming

ii. In a multi-source program, there is fileA.c that contains variables and functions, and a fileB.c that contains the main function, as well as usage of some of the resources found in fileA.c.

Explain:

a) fileA.c has a global variable called my_variable, that should only be accessed within the file. I.e., no other files should be able to access that variable. How should my_variable be declared inside of the file, in order to guarantee this functionality?

b) fileA.c also has a global variable called my_shared_variable, which can and should be accessible from other files, including fileB.c. How should my_shared_variable be declared in order to allow this functionality?