One Might Expect That Classical Conditioning Was Discovered by a Psychologist

One might expect that classical conditioning was discovered by a psychologist. However, it was discovered by a

A) physician who was studying the age at which children start to walk.
B) physiologist who was studying memory processes in monkeys.
C) physiologist who was studying digestion.
D) dog trainer who was trying to come up with the best way to reward animals for their performances in his shows.
E) neurologist who was studying unconscious motivations behind behaviors.