Which of these values for P and a will cause the function f(x) = Pa^x to be an exponential growth function?

Which of these values for P and a will cause the function f(x) = Pa^x to be an exponential growth function?

A. P= 13; a = 1/6
B. P= 1/13; a= 6
C. P= 1/13; a = 1/6
D. P= 13; a = 1