考研英语中的从句主要包括 主语从句、宾语从句、定语从句和状语从句。以下是各类从句的基本结构和用法：

主语从句

结构：主语从句通常由连接词如that, what, whether, if等引导。

例子：

That she is a rich woman is known to us all.

What he told me was only half-truth.

宾语从句

结构：宾语从句通常跟在动词或介词后面，可以用连接词如that, whether, if引导，that引导时通常可以省略。

例子：

I believe that she is a great singer.

Whether he will come is uncertain.

定语从句

结构：定语从句是用来修饰名词或代词的从句，通常由关系代词（如that, which, who, whom, whose等）或关系副词（如when, where, why）引导。

例子：

The book which is on the table is mine.

The person who called you is my friend.

状语从句

结构：状语从句是用来修饰动词、形容词、副词或整个句子的从句，通常由连词如when, while, before, after, because, since, if, although等引导。

例子：

If it rains tomorrow, we will stay at home.

Although he was tired, he kept working.

在写作中，正确使用从句可以增强句子的表达力和逻辑性。建议多练习不同类型的从句，注意连接词的选择和从句的结构，以提高语言表达的准确性和丰富性。