If f(x) is an antiderivative of g(x), and g(x) is an antiderivative of h(x), then
a. f"(x)=h(x)
b. h"(x)=f(x)
c. none of the above

If f(x) is an anti-derivative of g(x), then g(x) is the derivative of f(x). Similarly, if g(x) is the anti-derivative of h(x), then h(x) must be the derivative of g(x). Therefore, h(x) must be the second derivative of f(x); this is the same as choice A. 

I hope this helps.