Answer:
Bell- since the neutral stimulus becomes the CS
Step-by-step explanation:
Conditioned stimulus: The term "conditioned stimulus" is a part of the classical conditioning experiment, which was proposed by Ivan Pavlov.
In classical conditioning, the conditioned stimulus is defined as the formerly neutral stimulus after being associated or connected with an unconditioned stimulus, it triggers a conditioned response. The term conditioned stimulus is also referred to as CS.
In the question above, the CS is Bell- since the neutral stimulus becomes the CS.