A cup of water was enough to . . . . . . . . his thirst.

The correct answer is C. quench.

To quench one’s thirst is to satisfy it by drinking something. The other options are not as accurate.

• To satisfy something is to fulfill it or meet its requirements.
• To appease someone is to calm them down or make them less angry.
• To extinguish a fire is to put it out.

In this case, the man’s thirst was quenched by drinking a cup of water.