Don's Parents Want to Him to Do More Chores Around

Don's parents want to him to do more chores around the house so they decide to pay him a small amount (50 cents) for each chore he does. Initially, this produces a large increase in the number of chores that Don does, but his parents soon tire of paying him for his work and discontinue the monetary reward program. Don continues his chores for a short while but once he realizes that he's no longer being paid, he stops doing them all
Together. The discontinuing of Don's chore behaviour best illustrates the process of:

A) positive reinforcement.
B) habituation.
C) negative reinforcement.
D) operant extinction.