Ms. Pillar wants to teach Thurston to remain on task. However, she wants Thurston to remain on task during a variety of activities. Therefore, Ms. Pillar uses various materials during training such as staying on task doing paper work and at the table doing art work. What principle of generalization programming is she employing?

A) use of sufficient response exemplars
B) use of indiscriminable contingencies
C) reinforcing unprompted generalizations
D) use of sufficient stimulus exemplars