A: The decrease in the amount of daylight in winter causes a change in gene expression, which results in the foxes growing a lighter-appearing coat.
B: The diet of the foxes in summer lacks a particular nutrient, which causes the foxes to lose their white coat and grow a darker colored coat.
C: Competition for mates in the spring causes each fox to increase its camouflage with the environment by producing a darker-appearing coat.
D: The lower temperatures in winter denature the pigment molecules in the arctic fox coat, causing the coat to become lighter in color.