Fabian ordered chicken from a national chicken chain restaurant and became very ill immediately after eating it. Years later, Fabian still feels queasy when he sees an advertisement for the chicken chain or drives by one of its establishments. In this example, the unconditioned stimulus is the:
the bacteria that caused the illness. T/F

True.

Explanation:

Classical conditioning may be defined as the form of learning that in which the neutral stimulus combines with the unconditioned stimulus and generates a strong immune response.

The neutral stimulus is the previously present stimulus in the environment and  unconditioned stimulus is the stimulus that do not require any learning to show the response. In the given case in the question, the bacteria acts as the unconditioned stimulus because it is often to create the response of illness.

Thus, the answer is true.