V．单项选择（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答案。
21. —______ do you surf the Internet?
—Twice a week.
A. How far B. How soon C. How often D. How long
22. —What’s the matter _______ you?
— I’m not feeling _________.
A. on; good B. with; well C. to; healthy D. of; health
