The Use of DDT as an Insecticide in the United

The use of DDT as an insecticide in the United States has been outlawed since 1971, yet it is still a problem for certain top-level carnivores in the United States. Which of the following choices best explains this apparent incongruity?

A) DDT is still used for mosquito control in tropical countries, and certain migratory predators can be affected by a seasonal biomagnification.
B) DDT is persistent in the environment, and all of the pre-1971 DDT is still available in toxic form to poison top-level carnivores.
C) Pre-1971 DDT has been deposited in certain habitats, particularly wetlands and estuaries, so predators in these ecosystems are vulnerable to biomagnifications of DDT.
D) Whereas most DDT-susceptible species have become resistant to persistent DDT, others are still vulnerable.