Pavlov Placed Meat Powder in the Mouths of the Dogs

Pavlov placed meat powder in the mouths of the dogs, and they began to salivate. Pavlov's student noticed that after a few days the dogs began to salivate at the sound of the student's footsteps.The salivation to the sound of the footsteps was a _______.

A) primary reinforce
B) positive reinforcer
C) conditioned response
D) secondary reinforcer