Final answer:
A discriminative stimulus is a specific stimulus that signals the presence of reinforcement. The best example of a discriminative stimulus is a cat meowing for food when the can opener starts.
Step-by-step explanation:
A discriminative stimulus (SD) is a specific stimulus that signals the presence of reinforcement, indicating that a particular response is likely to be followed by a reward or punishment. The best example of a discriminative stimulus (SD) is option D) A cat meowing for food when the can opener starts. This is because the sound of the can opener serves as a signal that food is about to be provided, and the cat's meowing behavior is likely to be reinforced with food. The other options do not meet the criteria of a discriminative stimulus (SD) as they do not clearly signal the availability of reinforcement.