In Anticipation of Going Outside, Tara's Dog Started to Wag

Multiple Choice

In anticipation of going outside, Tara's dog started to wag his tail at the sound of the leash being picked up. Now Tara's dog has also started to wag his tail at the sound of the closet door being opened, where the leash is stored. The dog wagging his tail in response to the closet door being opened BEST exemplifies:

A) discrimination.
B) spontaneous recovery.
C) vicarious conditioning.
D) higher-order conditioning.