单项选择（共15小题；每小题1分，满分15分）
请认真阅读卜面各题，从题中所给的A, B, C, D四个选项中，选出最佳选项，并在
答题纸上将该项涂黑。
21．Weibo as well as WeChat＿＿as a media platform for people to share their thoughts
instantly without limits of place or time.
A. serves B. is served C. serve D. are served
22.＿＿t heir cultures, Americans have taken over from the Indians many other things.
A. On behalf of B. In praise of C. In possession of D. On top of
23．Students are advised to keep the list of books near the desk for easy＿＿·
A. preference B. function C. purpose D. reference
