In pavlov's classical conditioning experiment, he presented the sound of a bell along with meat powder to his dogs. after several trials, the dogs learned to salivate to the sound of the bell in the absence of the meat powder. in this study, meat powder acted as a(n)

The answer to this question would be: a) an unconditioned stimulus (UCS)

In Pavlov experiment, the meat is an unconditioned stimulus (UCS) because it doesn't need any learning. The meat will cause increased saliva production in the dog is it was reminding it of food. The bell, in this case, is conditioned stimulus because the dog learns the connection of the bell with the food.