The options are:
A. When they visit a doctor
B. When their house burns down
C. When their possessions are stolen
D. When they get their car repaired after an accident
And the correct answer is A) When they visit a doctor. The doctors are paid for their experience, not for the severeness of the illness of a patient. As we can see observe, in other options there is some amount of money that has to be paid and this amount is an exact amount. However, in the case of doctors because of the professionalism of the doctors this amount changes in accordance with expertise.