第二题：单项填空（共15小题；每小题1分，满分15分）
从A、B、C、D四个选项中选出可填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. I used to drink a lot of coffee, but these days I _____ tea.
A. prefer B. am preferring C. have preferred D. preferred
22. — Have you seen my glasses?
— Yes, I _____ them on your desk a minute ago.
A. see B. saw C. have seen D. had seen
23. — Would you care for a cup of coffee?
— I _____ one. Thank you just the same.
A. have had B. had C. would have D. will have
24. By the late 1960s, their style of music _____ completely.
A. changed B. have changed C. had changed D. was changed
