The standard form for an exponential function is
![y=a(b)^x](https://img.qammunity.org/2019/formulas/mathematics/high-school/24hx2tu6fgu3hvqzvzsb9ne4xmgcagoidm.png)
where is the initial value and b is the growth factor. If b > 1, then it is an exponential growth function, and if 0 < b < 1, then it is an exponential decay function. The b values that are greater than 1 are in A and C. The b values in B and D are greater than 0 but are less than 1 so those are decay. A and C are your answers.