Black squirrels are the same species as gray squirrels. A single litter of squirrels can have both black and gray squirrels. Over the past century, the percent of squirrels in the vicinity of Washington, DC, that are black instead of the more common gray has been continually increasing. Which of the following statements best explains why this is happening? A. Gray squirrels are more comfortable with humans than black squirrels. B. Black squirrels have a survival advantage over gray squirrels. C. Black squirrels are more visible against tree trunks than gray squirrels. D. Black squirrels are more popular with tourists than gray squirrels.