Answer:
bell; meat powder; salivation
Explanation:
Ivan Pavlov: He was a Russian physiologist who discovered Classical Conditioning. While studying the digestive systems of dogs, he noticed that after the presentation of food the animals salivated naturally.
He demonstrated a study, in which while feeding the dogs he rang a bell. Soon the dogs salivated only after ringing the bell. Pavlov believed the dogs were exhibiting classical conditioning. He summarized that there's a neutral stimulus i.e the bell which will not produce a response itself as salivation does.