Answer:
The answer is a. UCS (Unconditioned stimulus).
Explanation:
In classical conditioning, a conditioned stimuls is associated with an unrelated consequence, called unconditioned stimuls. This produces a reaction known as conditioned response.
In the example, the smell of the perfume was associated with the kiss, which resulted in heavy breathing. It's important to realise that any neutral stimulus can become conditioned. This means, if Sue had worn any other perfume, Bobby would have reacted the same way.
