A previously neutral stimulus that is able to elicit a response similar to the unconditioned response as a result of being paired with an unconditioned stimulus is called a stimulus.

conditioned stimulus

Explanation:

The conditioned stimulus is the part of the classical conditioning. The conditioned stimulus is a neutral stimulus and its effect remains hidden or the subject may not show any response towards it for some reasons. This stimulus becomes associated with the unconditioned stimulus to trigger the response in the stimulus. For example food is the conditioned stimulus but the smell of food is the unconditioned stimulus. The food may appear less tempting to the subject but before showing the food to the subject the smell of food may attract the subject.

the answer to your question is b