单项选择题
听下面一段对话，回答第18至第21题。
W: Mr. Parker, when did you arrive home yesterday evening
M: At about 8 o’clock.
W: What did you do right after you entered your flat
M: Well, I washed my hands and then watched sports news.
W: When did you have supper
M: At about a quarter to nine, I guess.
W: Did you stay at home all evening
M: Yes.
W: But your friend said that he called you several times between 8 and 9. But you didn’t answer.
M: Well, I think I was in the bath at that time.
W: No, you weren’t. You were not even at home last night. You robbed a bank in James Street.
A. Employer and employee.
B. Teacher and student.
C. Customer and assistant.
D. Police and criminal.