英语知识运用（共两节，满分45分）
第一节：单项填空（共15小题；每小题1分，满分15分）
从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21. -- Could you be so kind as to close the window?
---___
A. With pleasure B. Go ahead C. Yes, please D. That's OK
22. We can never expect___ bluer sky unless we create ___ less polluted world.
A. a; a B. a; the C. the; a D. the; the
