主语从句与 it 形式主语
外研版选择性必修第三册 Unit 1 重点语法。
一、主语从句引导词分类
- 从属连词：
that：陈述事实，不作成分，无词义，但在句首主语从句中不可省略。- That he succeeded was beyond our expectation.
whether：表示“是否”，不可用 if 代替位于句首的主语从句。- Whether they will agree remains unknown.
- 连接代词：
what, whatever, who, whoever, which, whichever：在从句中充当主语、宾语或表语。- What we need most is time.
- 连接副词：
when, where, why, how：在从句中充当状语。- Why the dinosaurs died out is still being investigated.
二、形式主语 it 替代主语从句
为避免主语过长导致句子头重脚轻，常将主语从句后置，句首用 it 占位：
It is clear / obvious that...It is reported / believed / said that...It doesn't matter whether...