Final answer:
In conditioned taste aversion induced by wheel running, 'wheel running' is the unconditioned stimulus (US) and 'taste' is the conditioned stimulus (CS). The response occurs when the taste is associated with the discomfort caused by wheel running.
Step-by-step explanation:
In conditioned taste aversion, specifically one induced by wheel running as mentioned in the question, the unconditioned stimulus (US) is actually the wheel running, because it is the event that naturally and automatically generates a response without prior learning involved. The conditioned stimulus (CS) is the taste, which only becomes a trigger for the response through its association with the unconditioned stimulus (wheel running) during the learning process. The answer to the question then is: a) Wheel running; Taste. This type of learning is important from an evolutionary perspective, as it helps organisms to quickly learn to avoid harmful foods and thus contributes to the survival of the species.