The pesticide ddt was widely used in the 1940s as a method of insect control. in the late 1950s the first ddt-resistant mosquitoes were discovered, and eventually ddt-resistant mosquitoes were found globally. when ddt is used now, the development of ddt resistance in mosquito populations occurs in months rather than years.

which of the following best explains the observations concerning ddt resistance in mosquitoes?
a. competition for limited resources causes mosquitoes to migrate to geographical areas that have richer supplies of ddt
b. the proportion of ddt-resistant mosquitoes in a population remains constant due to the metabolic costs of ddt utilization
c. natural selection favors ddt-resistant mosquitoes that are already present in a population when ddt exposure occurs
d. ddt is a chemical signal that delays normal reproductive cycles in many mosquito populations