Answer:
D) Ivan Pavlov, who studied classical conditioning
Step-by-step explanation:
Classical conditioning: In psychology, the term classical conditioning is determined as a learning theory which was proposed by Ivan Pavlov. In classical conditioning theory, a "conditioned stimulus" or CS tends to get connected with an unrelated or unlearned "unconditioned stimulus" or UCS to give rise to a "behavioral response" referred as a "conditioned response" or CR (learned response of formerly neutral stimulus).
In the question above, Molly's efforts most resemble the studies of "Ivan Pavlov, who studied classical conditioning".