一、 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选项。
(   )1. We’d better get ready for the dinner now because _________ Greens are coming to visit us tonight.
     A. a     B. an     C. the     D. /
(   )2. The plane will take off _________ three hours. I must get to the airport right now.
     A. in     B. for     C. on     D. at
(   )3. They _________ play football last Friday because Simon forgot to bring his football here.
     A. could     B. couldn’t     C. can’t     D. can