Final answer:
In classical conditioning, a 'neutral stimulus' is the correct answer as it is initially a stimulus that does not elicit any unlearned response from the organism.
Step-by-step explanation:
In a classical conditioning experiment, a neutral stimulus would likely serve as a stimulus that initially does not elicit any response from an organism.
Through the process of conditioning, this neutral stimulus can become associated with an unconditioned stimulus (UCS) which naturally elicits an unconditioned response (UCR). A well-known example is Pavlov's experiment with dogs, where the sound of a bell (neutral stimulus) was paired with the presentation of food (unconditioned stimulus), eventually leading to the sound of the bell alone causing the dogs to salivate (conditioned response).
Therefore, the correct answer to the question would be b) neutral stimulus, because before conditioning, it is a stimulus that does not naturally lead to the salivation response.