Which of the following versions of sentence(reproduced below) best previews the line of reasoning in the passage?

Though so different, both species domesticated themselves by joining humans for their own benefit and providing benefits in return, thus ensuring their places beside humans.

a. (As it is now)
b. However, because cats and dogs are so dissimilar in their behaviors, many people prefer one animal to the other.
c. Yet when we look further back in their history, both cats and dogs share a common ancestor: a mammal of the order Carnivora.
d. While dogs may be the oldest companion species of humans, this does not necessarily mean that cats are less thoroughly domesticated than dogs are.
e. Obtaining access to a steady supply of food is crucial to the story of domestication for both species.