Final answer:
D. unconditioned stimulus. An individual's irrational fear and anxiety in a phobia is known as a conditioned response, which is learned through classical conditioning when an originally neutral stimulus is associated
Step-by-step explanation:
When an individual has a phobia, the irrational fear and anxiety that the person experiences is known as a conditioned response. This occurs in classical conditioning, where a conditioned stimulus that previously did not cause fear becomes associated with fear through pairing with an unconditioned stimulus that naturally elicits an anxiety response. Over time, the individual begins to show the fear response to the conditioned stimulus alone.
For instance, in the famous case of Little Albert, a neutral stimulus (white rat) was paired with a loud noise causing fear (unconditioned stimulus), and eventually, Little Albert developed a fear of the white rat (conditioned response) without the noise. Therefore, in the context of phobias, the anxiety and fear are learned responses that have been conditioned.