The words- pal, buddy and companion carry a similar meaning -friend. A pal is a friend. A buddy is a close friend. A companion is a person or animal with whom one spends a lot of time or with whom one travels. He is a friendly person. However, a rival is a person competing with another for the same objective or for superiority in the same field of activity. He is not a friend. Hence, option C is correct and the other options are incorrect.