Answer: d. DDT bioaccumulates
Explanation: Bioaccumulation is the entry of pollutants such as metals into a food chain. Substances such as perchlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) are potentially dangerous over a period of time as it accumulates. DDT concentration is calculated in parts per million.
Biomagnification on the other hand is the build up of toxins in a food chain. An increase in the trophic level in a food chain results to an increase in the amount of toxic build up.