When a CS is not paired with a US,the subsequent fading of a CR is called

A) discrimination.
B) generalization.
C) secondary conditioning.
D) extinction.

Extinction

In psychology, the gradual weakening of a conditioned response when the conditioned stimulus is repeatedly presented without the unconditioned stimulus.

CS

In the context of classical conditioning, CS stands for Conditioned Stimulus, which is a neutral stimulus that, after being repeatedly paired with an unconditioned stimulus, begins to evoke a conditioned response.