Bryson is trying to train his pet parrot to say "Hello!" to him when he walks in the front door. Bryson has decided to motivate his parrot by using crackers as reinforcement. Which of the following reinforcement methods would be the least resistant to extinction?

A. Giving the parrot a cracker after every time it says "Hello!" when Bryson walks in the door.
B. Giving the parrot a cracker after it says "Hello!" when Bryson walks in the door an average of four times.
C. Giving the parrot a cracker for saying "Hello" once each 20 minutes.
D. Giving the parrot a cracker after every 4 times it says "Hello!" when Bryson walks in the door.