2. 常见的存在省略的状语从句：

　(1)when, while, as, until引导的时间状语从句。

　(2)if, unless, once引导的条件状语从句。

　(3)though, although, even if, even though引导的让步状语从句。

　(4)as though, as if, as引导的方式状语从句。

　(5)than引导的比较状语从句。

1. (2016·浙江)Had the governments and scientists not worked together, AIDS-related deaths __________ since their highest in 2005.

　A. had not fallen B. would not fall

　C. did not fall D. would not have fallen

2. (2015·江苏)It is so cold that you can't go outside __________ fully covered in thick clothes.

　A. if B. unless C. once D. when

3. -I hate talking with that guy. Look, he is coming. What should I do?

　-Don't speak until__________.

　A. speaking B. spoken to

　C. spoken D. speaking to

4. I wonder why you won't do it as__________. Its the third time you have done so.

　A. told to B. be told

　C. told you D. you told

5. Mr. Black, __________ born in Kentucky, lived and practiced law in Missouri.

　A. was B. he was

　C. although D. who he was

6. He broke his legs while __________.

　A. riding B. ride

C. was riding D. rode