Question: Biologists have discovered that the beluga whales of Canada's St. Lawrence River have the highest rates of cancer among animals. What is most likely the reason for this high incidence of cancer in these whales?

  Options: 
 A. chemical and pollutant runoff into the ocean
 B. average temperatures increased in the region
 C. depletion of natural prey from the ecosystem
 D. increased levels of carbon dioxide in the atmosphere
Answer: A