After His Mother Smiles,Jimmy's Request for a Snack Is Reinforced

Multiple Choice

After his mother smiles,Jimmy's request for a snack is reinforced.But if his mother is not smiling,his subsequent request for a snack is not reinforced.By indicating that Jimmy's request for a snack will be reinforced,the mother's smile is a(n)

A) primary reinforcer.
B) discriminative stimulus.
C) respondent behavior.
D) unconditioned response.