Amau Was Often Late to Work, Despite His Manager, Ebba

Amau was often late to work, despite his manager, Ebba, warning him against it several times. As a last resort, Ebba reduced Amau's salary in proportion to the hours he missed at work by being late. It turned out to be the right thing to do, as Amau was never late to work after the incident. This scenario is explained by

A) instrumentality.
B) valence.
C) positive reinforcement.
D) negative reinforcement.