Answer:
Conditioned stimulus.
Step-by-step explanation:
The conditioned stimulus is a previously neutral stimulus that, after becoming associated with the unconditioned stimulus will overtime trigger a conditioned response.
That means, what before was neutral (pulling into The Pizza Shoppe parking lot) will eventually be associated with the unconditioned stimulus (in this case is Molly feeling happy when she has pizza, what is a natural response) and becomes a conditioned stimulus making Molly happy for anticipation.
So, in this example, The Pizza Shoppe parking lot is the conditioned stimulus.