21. This agreement may be ____ six months before its expiry.
A. expanded
B. renewed
C. postponed
D. prolonged
22. The bank on the buyer‘s side in collection arrangement is the ____.
A. remitting bank
B. collecting bank
C. opening bank
D. notifying bank
23. Which of the four choices is NOT an appropriate response to the following sentence：" Do you mind opening the windows？" ____.
A. Surely not
B. Not at all
C. That‘s all right
D. No， of course not