Which of these values for p and a will cause the function f(x)=Pa^x to be an exponential growth function?
A.P=4;a=1/5
B.P=1/4;a=5
C.P=1/4;a=1/5
D.P=4;a=1
A.P=4;a=1/5
B.P=1/4;a=5
C.P=1/4;a=1/5
D.P=4;a=1