There are two variations of a species of peppered moth. One is a very light gray and the other is black. All the moths live on trees with white bark. What is most likely to lead to more black moths and fewer gray moths?
a. Air pollution stains the tree bark a darker color.
b. New predators are introduced and eat more moths.
c. Drought kills many of the trees
d. A contagious disease kills many of the moths