For a few months, the function f(x) = 15(3)^x represented the number of bees in a new hive x months from the time it was started. How did the number of bees change each month?

A. The number increased by 15 each month.
B. The number increased by 3 each month.
C. The number tripled each month.
D. The number increased by a factor of 15 each month.