Which situation best illustrates the concept of a discriminative stimulus?

The concept of a discriminative stimulus is best illustrated by the scenario involving a light that signals it's time for an exam. In the context of behavior analysis, a discriminative stimulus is a specific cue or signal that indicates the availability of reinforcement following a particular behavior.

In this example, the light serves as a clear indication to students that they should be prepared to take an exam, which may involve behaviors such as focusing, answering questions, or working independently. The light effectively sets the occasion for these target behaviors by signaling that reinforcement (such as a grade or praise) will follow the appropriate responses during the exam period.

This situation aligns perfectly with the definition of a discriminative stimulus: it precedes the behavior and provides information about when certain behaviors will be reinforced. Thus, when the light is on, it implies that engaging in specific behaviors related to the exam will lead to reinforcement, making it a prime example of a discriminative stimulus.