Mr. Johnson wants a hyperactive boy to be able to sit quietly for at least 15 minutes at a time. To do this, he begins praising the boy for sitting still for one minute, then for two minutes, and then only for four minutes, and so on. Mr. Johnson's strategy reflects which one of the following concepts?
a. Shaping
b. Generalization
c. Discrimination learning
d. Intermittent reinforcement
