Final answer:
The depth of anesthesia is judged by a patient's response to pain, which is indicated by changes in heart rate or blood pressure, as the sympathetic response is suppressed under anesthesia.
Step-by-step explanation:
The depth of anesthesia is determined by the patient's response to painful stimuli and is often judged by the sympathetic response. The correct answer is c. A change in heart rate or blood pressure. This is because general anesthetics suppress the body's autonomic responses to noxious or painful stimuli. When anesthesia is deep, the body does not exhibit a sympathetic response to pain, which would normally include an increase in heart rate and blood pressure. Observing the patient's autonomic functions like heart rate and blood pressure allows medical professionals to assess the depth of anesthesia and ensure the patient does not feel pain during surgery.