I. 单项选择：(共50题；满分50分；每小题1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，并在答题卡上将该项涂黑。
1. --- I serve three meals every day and do almost everything for him, but he still lets me down.
--- I’m afraid that’s ______ you are mistaken.
A.how B. where C. what D. in which
We will debate the subject_____ late when we have enough time.
| A．in vain | B．at length | C．at last | D．in force |
We will debate the subject_____ late when we have enough time.
| A．in vain | B．at length | C．at last | D．in force |
We will debate the subject_____ late when we have enough time.
| A．in vain | B．at length | C．at last | D．in force |
While watching television, __________.
| A．the doorbell rang | B．the doorbell rings |
| C．we heard the doorbell ring | D．we heard the doorbell rings |
John, look at the time. ___________ you play the piano at such a late hour?
| A．Must | B．Can | C．May | D．Need |