I'm taking the placement test of college and this is one of the study questions.

How do I figure this out?

If the function f satisfies the equation f(x+y)=f(x)+f(y) for every pair of real numbers x and y, what are the possible values of f(0)?

A. any real number

B. Any positive real number

C. 0 and 1 only

D. 1 only

E. 0 only