Understanding Classical Conditioning Responses

In classical conditioning, individuals learn to associate an originally neutral stimulus with an unconditioned stimulus that naturally triggers a specific response. One famous example of classical conditioning is Pavlov's experiment with dogs, where he paired the sound of a bell (neutral stimulus) with the presentation of food (unconditioned stimulus). After several pairings, the dogs began to salivate at the sound of the bell alone, demonstrating a conditioned response. Which of the following best describes the process by which the dogs learned to salivate in response to the bell?