Final answer:
In Pavlov's experiments, the dog's salivation to the bell's sound is the conditioned response, and the bell's sound itself is the conditioned stimulus; hence, the correct answer is option 4.
Step-by-step explanation:
In the classical conditioning experiments conducted by Ivan Pavlov, the salivation of the dogs in response to the sound of a bell represents the conditioned response and the bell represents the conditioned stimulus. Initially, the unconditioned stimulus was the food that naturally caused the dogs to salivate, this salivation being the unconditioned response. Through repeated pairings, the previously neutral stimulus, the bell, when consistently paired with the food, became associated with it, leading the dogs to salivate merely at the sound of the bell alone. Thus, the correct answer to the student's question is option 4) Conditioned response and conditioned stimulus.