The correct option is A A
The pyramid shows aquatic food chain, level D represents phytoplanktons, the primary producers, level C represents primary consumers zooplanktons, level B and A in the pyramid represents secondary consumers and top consumers respectively. Biological magnification is an accumulation of substances over subsequent trophic levels in the food chain and the top consumer exhibit largest quantity of accumulated substances as compared to those present at lower trophic level. In the given food chain, level A represents the top consumers and will be affected most adversely. Thus, the correct answer is option A.