Let f and g be twice differentiable real-valued functions defined on $\displaystyle \mathbb{R}$. If f'(x)>g'(x) $\displaystyle \forall x>0$, which of the following must be true for all x>0?

(a) f(x)>g(x)

(b) f''(x)>g''(x)

(c) f(x)-f(0)>g(x)-g(0)

(d) f'(x)-f'(0)>g'(x)-g'(0)

(e) f''(x)-f''(0)>g''(x)-g''(0)

The answer is c but I thought it was d. Can someone show me how to prove it is c?