Answer:
A. conditioned stimulus (CS)
Step-by-step explanation:
Conditioned stimulus: In psychology, the term conditioned stimulus is also denoted as CS, and is one of the important parts in the classical conditioning theory. The conditioned stimulus is defined as a formerly neutral stimulus that triggers a conditioned response once it gets associated or connected with the UCS or unconditioned stimulus.
In other words, the conditioned stimulus is initially a neutral stimulus that produces conditioned response.after getting attached to UCS.
In the question above, the dog's salivation to the sound of the bell is called the conditioned stimulus.