Answer: True.
Step-by-step explanation:
In behavioral psychology, stimulus control refers to a behavior that happens as a response to the appearance of a given stimulus. Likewise, a different behavior occurs in the absence of that stimulus.
In this example, the client´s behavior of stoping whatever he´s doing to turn to Bobby is controlled by the stimulus of Bobby entering the room. As a stimulus that alters behavior, Bobby entering the room is a discriminative stimulus.