Final answer:
Erin's response to the doctor's parking lot is due to classical conditioning, where she has learned to associate the doctor's office with receiving a shot, leading to crying.
Step-by-step explanation:
Erin's response of tensing and crying when her mother pulls into the doctor's parking lot after several visits that involved receiving a shot is due to classical conditioning. In classical conditioning, an organism learns to associate events that repeatedly happen together. In Erin's case, the doctor's office (a neutral stimulus) has become associated with the act of getting a shot (an unconditioned stimulus) that naturally leads to crying (an unconditioned response). Now, just the sight of the doctor's parking lot triggers Erin's tense and crying response (a conditioned response).
Operant conditioning, on the other hand, involves learning to associate a voluntary behavior with its consequences. Since Erin's reactions are reflexive and not voluntary behaviors that are strengthened or weakened by consequence, the correct answer to Erin's learning process is not operant conditioning but classical conditioning.