When Pavlov Placed Meat Powder in the Mouths of Canine

Multiple Choice

When Pavlov placed meat powder in the mouths of canine subjects, they began to salivate. His student noticed that after being brought to the laboratory a number of times, the dogs would begin to salivate at the sound of the person's footsteps. The footsteps acted as a/an:

A) unconditioned stimulus.
B) conditioned response.
C) unconditioned response.
D) conditioned stimulus.