It is not B or C because those answers would INCREASE the competition for food amount chipmunks. It cut off what answer choice D is supposed to be. But I think the answer choice might be A because if the chipmunks were to start dying off due to the epidemic, there would be less chipmunks to compete against for food. So the answer is A. Of course this is my opinion so if I am wrong, please feel free to correct me.