Answer:
The answer is B) an unconditioned stimulus.
Step-by-step explanation:
In classical conditioning, a conditioned stimulus (for example, the sound of a bell) is associated with an unconditioned stimulus (the meat powder). This produces a reaction known as conditioned response (the salivation).
It's important to understand that unconditioned stimulus are those that naturally produce a response, such as food = salivation. These are paired with another unrelated stimulus in order to condition a person or animal to respond in the same way.