Rachel has found that when she opens the cupboard door to get the cat food, the cats come running to the kitchen. rachel knows that this is classical conditioning and that the conditioned stimulus is the

The conditioned stimulus is to open the cupboard door.

Explanation:

Classical conditioning was developed by Ivan Pavlov. It consisted of associating two different stimuli to achieve the same response in a conditioned and unconditioned way.

In this case, the presence of cat food induces the unconditional response that cats come running. After several repetitions, the cats begin to associate that, when Rachel opens the cupboard door, it means they will have food. So there comes a time when the cats will come running only with Rachel opening the cupboard door:

- Unconditional stimulus (cat food) = Unconditional response (Cats come running into the kitchen).

- Conditioned stimulus (Rachel opens cupboard door) + Unconditional stimulus (cat food) = Unconditional response (Cats come running to the kitchen).

- Conditioned stimulus (Rachel opens cupboard door) = Conditioned response (Cats come running to the kitchen).