Answer:
The anwer is conditioned stimulus.
Explanation:
In classical conditioning, a conditioned stimulus (the sound of the bell) is associated with an unrelated consequence, called unconditioned stimulus (the shock). This produces a reaction known as conditioned response.
It's important to recognise that any neutral stimulus can become a conditioned stimulus. For example, instead of the sound of a bell, it could be a flashing light that produces the same response.