When the insecticide (a chemical designed to kill insects) known as DDT was first introduced to insect populations, it was highly effective. Which of these is the most likely reason that DDT became less effective as an insecticide? A)changes in the types of crops grown caused changes in the types of pests

B)biological magnification decreased the number of insect predators

C)insects resistant to DDT survived and reproduced more successfully so the proportion of resistant insects increased over time

D)rain caused DDT to be washed away in water runoff