13. According to Rolle's Theorem, which of the following sets of conditions guarantees that there is a number c in (a, b) at which f(c) = 0? A. f is continuous within [a, b], f is differentiable within (a, b), and f(a) = ((b) B. fis continuous within (a, b), fis differentiable within (a, b), and f(a) = f(b) C. fis continuous within [a, b], f is differentiable within (a, b), and f(a)