Final answer:
d. B. F. Skinner uncovered the theory of the magic number 7. Skinner proposed the theory of operant conditioning.
Step-by-step explanation:
The correct answer is d. B. F. Skinner. Skinner proposed the theory of operant conditioning, which is a form of learning that involves changing behavior through reinforcement and punishment.
He developed the concept of a Skinner box, which is an operant conditioning chamber used to study behavior. Skinner's ideas had a significant impact on the field of psychology and are still influential today.