四、单项填空（共15分，每小题1分）
从下面各题所给的A、B、C、D四个选项中，选择可以填入空白处的最佳选项。
21. --- Excuse me. Can you tell _____ where the post office is?
--- Sure. Walk ahead, turn left and you will see it.
A. I B. me C. my D. mine
22. --- What do you usually do _____ the evening?
--- I watch the CCTV9 news, and do some revision work.
A. for B. on C. at D. in
