C .He  is ____ young  ____ he ____ go to school .

　　   D .He isn't ______ _______ ______ go to school  (Keys :B :such , that , can't C :so  ,that ,can't .D : old  ,enough  to )   

　　易错分析：

　　①关于not…until

　　He stayed there until it was very late.

　　句中，stay是可延续性动词，所以不用not。

　　He didn't leave until it was very late.

　　句中，leave是不可延续性动词，所以用not

　　②because, so；although, but

　　上面已经提到，because和so及although和but不连用。

　　例如:

　　Because he was late, he didn't catch the first bus.

　　一定不可以说

　　Because he was late, so he didn't catch the first bus.

　　③or还是and

　　祈使句＋or＋陈述句前后是对立的

　　祈使句＋and＋陈述句前后是统一的

　　(or或and后的陈述句，常用一般将来时)

　　Study hard, or you won't pass the exam.

　　Study hard, and you will pass the exam.

　　两句都可以转换成“If条件句＋主句”形式，注意：要去掉or和and：

　　If you don't study hard, you won't pass the exam.

　　If you study hard, you will pass the exam.

　　④because, since, as, for表示原因时的区别

　　尽管because, for, since, as都表示原因，但是用法上有不同.

　　because通常表示说话人认为这种理由或者原因是听话人所不知道的.

　　如:

　　He didn't attend the meeting because he had too much work to do.

　　since表示的原因是人们已知的事实，常译作“既然”。

　　如：

　　Since he can't answer this question, you'd better ask someone else.

　　as表示原因与since差别不大，只是语气更弱,多译为“由于”

　　如：

　　As I haven't seen the film, I can't tell you what I think of it.

　　for表示因果关系时，只能放在主句之后，不能放在句首。而且经常是对主句补充说明理由或推断原因。

　　如：

　　It rained last night, for the ground is wet.

　　⑤ as, when, while

　　这三个连词都可引导时间状语从句，但用法有所不同。
1) 当某事正在进行的时候，又发生了另一件事。While, when, as 都可用来引导表示“背景”的时间状语从句。例如：
As/When/While I was walking down the street I noticed a police car.
2) 当两个长动作同时进行的时候，最常用的是while。例如：
While mother was cooking lunch, I was doing my homework.
3) 当两个动作都表示发展变化的情况时，最常用的是as。例如：
As children get older, they become more and more interested in things around them.
4) 当两个短动作同时发生时，或表示“一边…一边…”时，最常用as。例如：
Just as he caught the fly, he gave a loud cry.
She looked behind from time to time as she went
5) 当从句的动作先于主句的动作时，通常用when。例如：
When he finished his work, he took a short rest.
6) 当从句是瞬间动作，主句是延续性动作时，通常用when。例如：
When John arrived I was cooking lunch.
（6）if, whether
if和whether都可作“是否”讲，在引导宾与从句是一般可互换。例如：
I wonder whether (if) you still study in that school.
I don’t know whether (if) he likes that film.
   1) 引导主语从句时。例如：
Whether he will come to the party is unknown.
2) 引导表语从句时。例如：
The question is whether I can pass the exam.
3) 在不定式前。例如：
I haven’t made up my mind whether to go there or not.