A young American doctor is asleep when his doorbell rings. It is late at night, but he has to put on his coat to answer it. It is a man! He is standing with a hat in his hand. "How do you do?" says the man. "Can you go with me now to a place out of the town? It is quite far from here, but I know you have a car and I can show you the way." "Certainly," says the doctor, "I can go with you now." The car is at the front door. The man gets into the doctor's car and they drive off. They drive for a long time, and finally the man says, "Here we are. This is my home. Now I give you money and you may go back." "But I must see the patient ," the doctor says. "How can I go back without seeing the patient?" "There's no patient," says the man, "nobody is ill. I live here. There is no taxi at this time, but a doctor often goes out for night calls . So, excuse me. Here is your money. Thank you, doctor. Good night!" The man gives the doctor money, because   _  .
the doctor is a good doctor the doctor takes him home late at night he is very rich the doctor sees a patient