DDT was sprayed over an area of land to control a population of insects. It is believed that the pesticide interfered with birds' ability to metabolize calcium. The best explanation for how this pesticide came to affect the eggshells of the birds is that:
A. Fish eaten by the birds had been directly sprayed with DDT
B. The birds were sprayed with DDT
C. DDT washed into local bodies of water, was passed through the food chain consisting of plankton, fish and the birds
D. Insects sprayed with DDT infested the birds' nests