Final answer:
A conditioned stimulus can eventually act as an unconditioned stimulus in a second round of conditioning through higher-order conditioning.
Step-by-step explanation:
In classical conditioning, a conditioned stimulus (CS) is initially paired with an unconditioned stimulus (US) to create a conditioned response (CR). Over time, if the CS is paired with a new neutral stimulus, it can become an unconditioned stimulus in a second round of conditioning. This is known as higher-order conditioning. For example, if a bell (CS) is repeatedly paired with a light (neutral stimulus) and then the light is paired with food (US), eventually the light alone can elicit a conditioned response.