Keystone predators (2 points)
a. play a small role in a food web.
b. are not part of a food web.
c. are always top predators.
d. play an important role in a food web.

By definition, a keystone predator is a predator that once it is eliminated from the food web, prey population thrives. This often leads to a decline in diversity within the food web. With this in mind, we can say that A and B are wrong. Additionally, from the information, we can say that D is the correct answer since they do play a very important role in the food web.