In _________original research, dogs heard a tone and then had meat powder placed in their mouths which caused them to salivate. After many pairings of the tone and the meat powder, they would salivate when the tone was presented alone. In this case, the tone is an example of _________
A. Pavlov's, conditioned stimulus
B. Watson's, operant conditioning
C. Skinner's, unconditioned stimulus
D. Bandura's, cognitive learning