Answer:
The answer is the sound of the can opener and the salivation, respectively.
Explanation:
In classical conditioning, a conditioned stimuls (the sound of the can opener) is associated with an unrelated consequence, called unconditioned stimuls (the food). This produces a reaction known as conditioned response (the salivation).
It's important to recognise that any neutral stimulus can become conditioned when constantly followed by a consequence. In the example, the sound of the can opener could be replaced by a bell, and in time would produce the same response.