Associative learning is best illustrated by

A) immediate gratification.
B) unconditioned responses.
C) positive punishment.
D) classical and operant conditioning.

Associative learning refers to the process by which we learn through the association of a stimulus with a particular response. Classical conditioning and operant conditioning are both forms of associative learning, in which we learn to associate stimuli with particular responses or behaviors. Therefore, D is the best choice as it specifically mentions both classical and operant conditioning as examples of associative learning.