Answer:
d) conditioned stimulus
Explanation:
Conditioned stimulus: The term has been first used in the classical conditioning experiment and can be widely applied in the day to day life.
Therefore, the conditioned stimulus in classical conditioning is a stimulus that was neutral earlier and after being associated with an unconditioned stimulus then it gives rise to a conditioned response.
In the question above, for the dogs, the sight of this person was a conditioned stimulus.