A Pigeon Has Been Trained to Peck a Dark Red

Multiple Choice

A pigeon has been trained to peck a dark red disk for food reinforcement. When the colour of the disk is switched to a lighter shade of red, the bird, at first, pecks infrequently. Soon, though, the pigeon pecks the disk at the rate at which it was pecking the darker disk. The pigeon's behaviour an example of

A) negative reinforcement.
B) discrimination.
C) generalization.
D) shaping.
E) habituation.