The population of a town after 1990 can be modeled by the expression I(1. 045)^t, where t represents the number of years since 1990 and I represents the population of the town in the year 1990. Which expression represents the monthly growth rate?
A I(1. 045^12)^12t
B. I(1. 045^12)^1/12t
C. I(1. 045^1/12)^1/12t
D. I(1. 045^1/12)^12t