Final answer:
The meatloaf is the Conditioned Stimulus (CS) in this scenario.
Step-by-step explanation:
In this scenario, the meatloaf would be the Conditioned Stimulus (CS).
According to classical conditioning, the unconditioned stimulus (UCS) is the meat powder that elicits a natural (unlearned) response, which is salivation (UCR). However, through repeated pairings of the meatloaf with unpleasant experiences, Mary has learned to associate meatloaf with those negative feelings. Therefore, the meatloaf becomes the conditioned stimulus (CS) that elicits an aversion or dislike for Mary, which is the conditioned response (CR).