在状语从句中，为了使语言更加简洁地道，经常运用省略的形式。SAT语法也会考查这一特殊的句式。状语从句的省略必须满足以下两个条件：

1.主句主语和从句主语一致，或从句主语为it

2.从句的谓语动词是be的某种形式

       状语从句满足上述两个条件的话，我们就可以把从句的主语和be动词全部省略，从而使语言更加简洁。状语从句的省略的具体规则如下：

1. 当状语从句的主语是it，且谓语动词是be时，省略it和be。

       If (it is) possible, he will help you out of the difficulty.

       You must attend the meeting unless (it is) inconvenient to you.

2. 当状语从句的主语和主句的主语一致，且谓语动词是be时，省略从句的主语和be动词。常用于以下几种情形：

      1）连词+形容词

       As (he was) young, he learned how to ride a bike.

       Whenever (she is) free, she often goes shopping.

       2）连词+名词

       While (he was) a young boy, he was always ready to help others.

       Although (he was) a farmer, now he is a famous director.

       3）连词+现在分词

       As (she was) walking along the river bank, she was singing a pop song.

       Although (he is) doing his best in English, he has still got no good marks.

       4）连词+过去分词

       He won't go there with us unless (he is) invited.

       The concert was a greater success than (it had been) expected.

       5）连词+不定式

       He stood up as if (he were) to say something.

       He wouldn't solve the problem even if (he were) to take charge.

       6）连词+介词短语

       She looked anxious as though (she was) in trouble.

       He had mastered the English language before (he was) in the USA.

       注意：当从句主语和主句主语不一致时，就不能使用状语从句的省略形式。这时，从句部分要么使用完整的形式，要么使用独立主格结构来表达。

When the meeting was over, all the people went out of the meeting-room.

(=The meeting over,）

After their lessons were finished for the day, the children went home from the grammar school.

(=Their lessons finished for the day,）

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