单项选择题

W: Can you come to my birthday party tomorrow afternoon, Uncle Denis
M: I’d like to, Christine, but I can’t. I’ll be in surgery at 3 o’clock. I’ll be seeing patients in my office at 5 o’clock.

What is this man’s occupation()

A.Salesman. 
B.Sportsman. 
C.Teacher. 
D.Doctor.