A、Classmates. B、Patient and doctor. C、Student and teacher. D、Colleagues. B由关键词“肠胃感染”，“测量体温和血压”，结合男士所说的“频繁去厕所”，推断谈话双方关系为病人和医生，选B。

W: I have to call Kate, and tell her about the interview tomorrow afternoon.
M: Why bother? You will see her this afternoon at the meeting.
Q: What does the man mean?

M: I have to go to the toilet quite frequently.
W: Well, it sounds as if you’ve picked up a stomach infection. Let’s check your temperature and blood pressure.
Q: What is the probable relationship between the two speakers?