In t'years, the population of a certain city grows from 500,000 to a size P given by P(t) = 500,000 + 7000t. a) Find the growth rate, dP dt b) Find the population after 20 yr. c) Find the growth rate at t=20. d) Explain the meaning of the answer to part (c). a) dP dt b) The population after 20 yr is (Simplify your answer.) c) The growth rate at t = 20 is (Simplify your answer.) d) What is the meaning of the answer to part (c)? O O A. The growth rate tells the difference between the rate of growth at the beginning of t = 0 and t = 20. B. The growth rate tells the average growth from time t=0 and t = 20. C. The growth rate tells the rate at which the population is growing at time t = 20 -1. D. The growth rate tells the rate at which the population is growing at time t = 20.