Sperm whales are found in oceans around the world and are known to have the largest brain of any organism. The head of a sperm whale takes up about one–third of its body. Another anatomical characteristic of a sperm whale are the hind leg bones circled below. In terms of evolution, which of the following statements best explains why the sperm whale has hind limb bones?

A: Ancestors of the sperm whale had hind legs to walk on land but the legs became useless when they moved to water.

B: Sperm whales began developing hind limbs to escape hunters and then hunting decreased as the population dwindled.

C: Sperm whales have legs when they are young and then they disappear since they are not needed in water.

D: Sperm whales are equipped with leg bones in case they need to move to land some day.