英语中as作为关系代词引导定语从句的用法

Answer 1

在英语中，as作为关系代词有多种用途，引导定语从句。以下是其主要用法的概述：

1. as引导非限制性定语从句，用来补充说明主句，常以"As is"句型呈现，相当于"which fact"。例如：

He left early, as was his habit.
As is commonly shown, plants require sunlight to grow.
As is often reported, exercise benefits overall health.

根据动词变化，某些as从句中的is可省略。关系代词as与which的区别在于，as强调“正如”，通常指代整个主句，而which可用于限制或非限制性从句，但通常位于句末。

2. 当先行词被the same, such, so, as等修饰时，as用于构成特定结构，如the same ... as, such ... as, so ... as, as ... as。例如：

He was so talented a musician as everyone admired.
She had the same laptop as her colleague.

值得注意的是，as引导的定语从句和as引导的比较状语从句，以及such ... as引导的定语从句和such ... that引导的结果状语从句有结构和含义上的差异。

在口语或非正式语境中，as有时可以替代which, who或that。例如：

That was not the car as he ordered.

总之，as在英语定语从句中的使用要根据上下文和结构来区分，它在补充信息、强调或构成特殊结构时发挥着重要作用。