In classical conditioning, the stimulus that naturally evokes an unlearned response is the

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

Unconditioned Stimulus

A stimulus that automatically triggers a response without any need for prior learning.

Conditioned Stimulus

A previously neutral stimulus that, after becoming associated with an unconditioned stimulus, eventually triggers a conditioned response.

Unconditioned Reinforcer

A stimulus that naturally and automatically triggers a response without any need for learning, such as food for a hungry animal.