It's a Very Hot Summer Day and Ai Is Sweating

It's a very hot summer day and Ai is sweating in her apartment. She turns on the air-conditioning and right away her apartment gets cooler. Ai is now more likely to turn on the AC when she is hot to reduce her discomfort; this is an example of

A) positive reinforcement.
B) negative reinforcement.
C) punishment.
D) a penalty.