John's Mother Wants Her Son to Stop Crying Every Time

Multiple Choice

John's mother wants her son to stop crying every time something goes wrong. Following a psychologist's advice, she stops running to comfort John whenever the boy starts crying over some minor incident. After a few weeks, she notices that John cries much less frequently than he used to. This is an example of

A) positive reinforcement.
B) negative reinforcement.
C) punishment.
D) extinction.