Respuesta :

You are multiplying by 3 each time. This sequence is geometric.

9 = 3*3 = 3^2

27 = 3*9 = 3*3*3 = 3^3

81 = 3*27 = 3*3*3*3 = 3^4

and so on.

The general rule is 3^x which is choice D