A local movie theater had small cups of popcorn sitting on the counter where patrons purchased tickets. The cups were called "complimentary cups," and their purpose was to promote the sale of popcorn. This procedure is most similar to:_________.
a. self-reinforcement.
b. generalized reinforcement.
c. intermittent reinforcement.
d. reinforcer sampling.

Reinforcer sampling is the method of applying a reinforcer to an individual(s) that ensures the individual(s) acts in a particular desired way. The movie theater described in the question are making use of reinforcer sampling when placing little pop corns cups at the entrance of the theater, this helps as a trigger that propels the movie watchers to want to buy pop corns.