Which sentence might be found in a science textbook that explains why the arctic fox in this picture is white? a) the arctic fox rolls in the snow to keep its fur clean. b) since the arctic fox is usually brown, seeing a white one is quite rare. c) although grey when it is young, the arctic fox turns white as it gets older. d) the arctic fox has white fur that blends in with the color of the snow so that the fox's enemies cannot see it.