When Maurice's Father Walks Through the Door After the End

Multiple Choice

When Maurice's father walks through the door after the end of a long day at work, Maurice jumps up, claps his hands, and runs to see Daddy. Lately, though, he has been dropping his toys and getting excited when he hears his father's keys in the lock. The fact that the response has changed stimuli is a demonstration of

A) ​operant conditioning.
B) ​habituation.
C) ​the orienting response.
D) ​classical conditioning.