The correct answer is B. Detain : Suspect.
In the original pair of words, “confine” means to keep someone in a particular place, and “prisoner” means someone who is kept in a place of confinement. In the lettered pair B, “detain” means to keep someone in custody, and “suspect” means someone who is suspected of a crime. The relationship between “confine” and “prisoner” is the same as the relationship between “detain” and “suspect”: both pairs of words involve someone being kept in a place against their will.
The other lettered pairs do not have the same relationship. In pair A, “impeach” means to charge someone with a crime, and “president” means the head of state of a country. In pair C, “ambush” means to attack someone by surprise, and “sentry” means a guard. In pair D, “fear” means to be afraid of something, and “joy” means to be happy.