Problem 13. (6 points) 1. The temperature of a city t hours after 9:00 am is modeled (in degrees Fahrenheit) by the function T'(t) = 80 + 19 sin(at/12). According to the model, what is the average temperature over the time period from 9:00 am to 9:00 pm? O A. None of these O 12 B. 12 (80 + 19 sin(at/12) )dt O 21 C. 1 12 (80 + 19 sin(at/12) dt O 12 D. (80 + 19 sin(at/12))dt O (80 + 19 sin(at/12))dt