By pairing the ringing of a bell with the presentation of meat, pavlov trained dogs to salivate to the sound of a bell even when no meat was presented. in this experiment, the presentation of the meat was the:

Unconditioned stimulus.

Explanation:

Classical conditioning may be defined as a type of learning procedure in which the biological procedure is used to pair up with the previous nerve stimulus. This stimulus result in the response of an individual.

The Pavlov experiment with the dog explains the process of classical conditioning. The ringing of bell (conditioned stimulus) is paired with unconditioned stimulus (meat presentation).

Thus, the meat presentation is unconditioned stimulus.

the answer to your question is:

c. complementary base-pairing