While Out Trick-Or-Treating for Halloween, at First Billy's Neighbours Had

Multiple Choice

While out trick-or-treating for Halloween, at first Billy's neighbours had to remind him to say "trick or treat" before they dropped their treats into his bag. As he continued to visit houses in the neighbourhood, soon Billy would say "trick or treat" as soon as the neighbours answered the door. The treats he received were the ____ for his saying "trick or treat".

A) conditioned stimulus
B) reinforcement
C) reward
D) discriminative stimulus