Given the task definition and input, reply with output. You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each 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?
(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
A