Health Economists Observe Individuals' Willingness to Pay by Observing Not

Health economists observe individuals' willingness to pay by observing not only cash transactions, but also by observing patients' time spent waiting and/or pain endured to obtain medical services. Examples of observable, non-cash prices paid by patients include all of the following, except

A) a caretaker waits nine months for a family member to receive nursing home care.
B) a patient undergoes experimental cancer vaccine to arrest the growth of a tumor.
C) a patient pays another patient $50 to trade places in the queue at the free clinic.
D) an elderly patient waits eight hours to see a doctor for free at a famous eye clinic.
E) a morbidly obese patient must undergo six months of nutrition counseling prior to undergoing surgery to induce weight loss.