Question

什么是限制性定语从句？

Answer 1

限制性定语从句与非限制性定语从句用法区别：
一、 句法功能、表现形式不同
定语从句分为限制性和非限制性两种。限制性定语从句不可缺少先行词，去掉它主句意思往往就不明确了，它与主句之间通常不用逗号分开；非限制性定语从句是对先行词的附加说明，去掉它也不会影响主句的意思。如：
Do you know the professor who is speaking at the meeting? （限制性定语从句）English is an important subject, which every student should study well. （非限制性定语从句）
二、 先行词不尽相同。限制性定语从句的先行词往往是某一个词，但非限制性定语从句的先行词可以是一个词，也可以是句子的一部分，甚至是整个主句，此时非限制性定语从句一般由which或as引导，as引导非限制性定语从句常用在as is said / known / expected / mentioned / reported / announced等结构中。如：
He has passed the college entrance examination, which makes his parents quite happy.
As is known to everybody, the moon travels round the earth once every month.