主语从句：在复合句中充当主语成分的句子叫做主语从句。常规主语从句，即句子在复合句中充当一个主语。主语从句的时态:不受主句的时态影响和限制。
例子：
That he finished writing the composition in such a short time surprised us all.
Whether we will go for an outing tomorrow remains unknown.
表语从句：连接表语从句的连接词有:that, what, who, when, where, which, why, whether, how, whoever, whomever, whichever, whatever等。还有如because, as if, though等。
例子：
He has become a teacher.
他已经成为一名教师。
He has become what he wanted to be ten years ago.
他已经成为了他10 年前想成为的职业。
宾语从句：宾语从句就是一个句子作动词或介词的宾语。宾语从句在复合句中作宾语，位于及物动词后。
例子：
Tell him which class you are in.
Do you know what he likes?
定语从句：用作定语的从句叫定语从句。定语从句一般皆放在被它所修饰的名(代)词之后，这种名(代)词就叫作先行词(Antecedent)。引导定语从句的关联词为关系代词(或称引导词、关系词等)。关系代词在定语从句中可用作主语、宾语、定语等;关系副词在定语从句中用作状语。
例句:
The dog that/which was lost has been found. (失踪的狗已经找到了。)。
Those who are in favor of the proposal are expected to discuss it in detail after the meeting. (有人认为那些对这个提案有兴趣的人最好是在会后再具体讨论它。)。
状语从句：用作状语的从句叫作状语从句，其关联词是一些从属连词。修饰主句中的动词、形容词和副词，通常由从属连词引导，按其意义和作用可分为时间、地点、 条件、 原因、让步、目的、结果、 方式、比较状语从句等。
时间状语从句
例句:
As you look at yourself in a mirror,you'll seen an identical image of yourself.