世纪金榜高中全程学习方略选修7单元质量评估(三) Unit21
---May I go and play with Tom this afternoon, Mom?
---No, you can’t go out ____ your homework is finished.

A. before    B. while  C. until   D. unless
答案是C，但是为什么不能选D。

解释：

until 表"直到", 强调时间的延续,引导时间状语从句。而unless表"除非", 强调条件,引导条件状语从句。上述题目中no 后用逗号，“you can’t go out” 承接否定词no，强调“你不能出去”的状态一直延续到“你作业被完成。”笔者认为：如果no 后用句号，可用unless，强调条件，意为：“如果你的作业未完成，你就不能出去。”例如：

1. I didn't know the news until my teacher told it to me.

动词 didn't know 表明该句强调时间的延续, 表"我不知道这消息"的状态一直延续到"老师告诉我", 因此应用until 引导时间状语从句。

2. I couldn't know the news unless my teacher told it to me.

动词couldn't know表明该句强调条件,表"我不可能知道这消息, 除非老师告诉我", 因此应用unless引导条件状语从句。

 练习：

1. Owen wouldn't eat anything ______ he cooked it himself.

   A. until　　　B. since　　　　C. unless　　　D. while

  【答案】C   【来源】09四川

2. We'll have a picnic in the park this Sunday _____ it rains or it's very cold.

   A. since      B. if         C. unless       D. until

  【答案】C   【来源】08天津

3. _____ you call me to say you're not coming, I'll see you at the theatre.

   A. Though      B. Whether        C. Until   D. Unless

  【答案】D   【来源】04全国2

4. ______ our manage objects to Tom's joining the club, we shall accept him as a member.

   A. Until         B. Unless       C. If     D. After

  【答案】B   【来源】10上海

5. All the photographs in this book, _______ stated otherwise, date from the 1950s.

   A. unless    B. until    C. once    D. if

  【答案】A   【来源】12陕西

6. A good storyteller must be able to hold his listeners' curiosity_____ he reaches the end of the story .

   A．when B．unless      C．after        D．until

  【答案】D   【来源】03上海春考

7. --- Was his father very strict with him when he was at school?

    --- Yes. He had never praised him _____he became one of the top students in his grade.

   A. after     B. unless C. until       D. when

  【答案】C   【来源】03北京春考

8. Simon thought his computer was broken ____ his little brother pointed out that he had forgotten to turn it on.

   A. until       B. unless        C. after          D. because

  【答案】A   【来源】05北京春考