Which of the Following Variations Could Be Subject to Natural

Which of the following variations could be subject to natural selection?

A) A dog with short legs due to malnutrition is able to crawl into holes better than his littermates.
B) A tree is not infested by a ground-dwelling beetle when the homeowner cuts the lower branches.
C) A hyena is born with a spotted fur pattern that allows it to hide in the grass better than its littermates.
D) A pigeon learns that when its keeper comes near it will get fed.