Which one of the following questions about population growth is the only true statement? a) the size of a population can never exceed the carrying capacity. b) if a population is at the carrying capacity of the environment, then the birth rate will more or less equal the death rate (i. e., zero population growth).c) a population that is growing according to the exponential growth model will always end up going to extinction (i. e., dying out).d) the carrying capacity of the environment is fixed and can never change. e) none of the statements are true, they are all false.