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 unconditioned stimulus is the .

Cat food

Explanation: In classical conditioning, whereby a conditioned stimulus becomes associated with an unrelated unconditioned stimulus in other to trigger a conditioned response, The conditioned stimulus could be thought of as stimulus which is initially neutral before being connected or associated with an unconditioned stimulus (stimulus which occurs naturally) to generate a conditioned response. The unconditioned stimulus occurs naturally, the usual example is usually the feeling of hunger felt when the smell of food is perceived, here there is no initial or man-made connection or association between the stimulus and the response. Here the unconditioned stimulus is the cat food and the conditioned stimulus is the opening of Cupboard.

answer; i do believe its (b) 12.5 years of age;