Every time Lucy dropped one of the store's imported chocolates on the floor, the manager yelled at her and made her wipe up the floor. As Lucy became less nervous, she dropped fewer chocolates and the manager yelled at her much less. In time, Lucy stopped dropping chocolates altogether. What principle did the manager use to change Lucy's behavior

negative reinforcement                      

Explanation:

Negative reinforcement: In psychology, the term "negative reinforcement" is described as one of the parts in the theory of operant conditioning and was proposed by B. F. Skinner.

Negative reinforcement is described as a phenomenon in which a specific behavioral response is being strengthened by ignoring, stopping, avoiding, removing a particular aversive stimulus or a negative outcome.

In the question above, the given statement signifies the "negative reinforcement".

i'll just take the points xd

the answer is true .