when非限定性定语从句用法
导语：关系副词when在非限制性定语从句中作时间状语，指代主句中表示时间的词语。下面是小编给大家整理的when非限定性定语从句用法的相关内容，希望能给你带来帮助!
非限定性定语从句起补充说明作用，缺少也不会影响全句的理解，它与主句往往用逗号隔开。定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开，将非限定性定语从句放在句子中间，其前后都需要用逗号隔开。
when非限定性定语从句用法
when引导
关系副词when在非限制性定语从句中作时间状语，指代主句中表示时间的词语。
如：He will put off the picnic until May 1st, when he will be free.
他将把郊游推迟到5月1号，那时他将有空。
where引导
副词where在非限制性定语从句中作地点状语，指代主句中表示地点的词语。
如：They went to London，where they lived for six months.
他们去了伦敦，在那儿呆了六个月的时间。
as引导
as引出非限定性定语从句时，代替整个主句，对其进行说明但通常用于像as we all know, as it is known, as is known to all, as it is, as is said above, as always mentioned above, as is usual, as is often the case, as is reported in the newspaper等句式中。as在非限定性定语从句中作主语、表语或宾语，且引出的'从句位置比较灵活，可位于句首或句末，也可置于主句中间。通常均由逗号将其与主句隔开。as有“正如……， 就像……”之意。
如：As is known to the United States, Mark Twain is a great American writer.
美国人都知道，马克·吐温是一位伟大的美国作家。（as在从句中作主语）
He forgot to bring his pen with him, as was often the case.
他忘了带笔，这是常事。（as在从句中作主语）
He is absorbed in work, as he often was.
他正在全神贯注地工作，他过去经常这样。（as在从句中作表语）
As we all know, the earth is round.
众所周知，地球是圆的。（as在从句中作宾语）
The two brothers were satisfied with this decision，as was agreed beforehand.
两兄弟对此决定都满意，这项决定在事前都已得到他们的同意。(as在从句中作主语)
Taiwan is，as you know，an inseparable part of China.
你知道，台湾是中国不可分割的一部分。(as在从句中作宾语)
“介词+关系代词”引导非限制性定语从句：在介词后引导非限制性定语从句。
难：句意相同
as it is known to all (that...) (as 做状语从句连词，是状语从句, 可以加that)
与 as is known to all (as做主语，是定语从句)
与 it is known to all that... (主语从句，it是形式主语)
即：As is widely known, the moon is closer to the us than the sun.(定从)
= That the moon is closer to the us than the sun is widely known.(主从)
= It is widely known that the moon is closer to the us than the sun.(主从)
As it is known to everyone, I thought you knew about it too.(状从)[1]
关系代词which有时并不代表主句中某一确定的词，而是概括整个主句的意思。介词的选择取决于它与先行词的搭配或与从句中谓语动词的搭配。
They were short of sticks to make frames for the climbing vines，without which the yield would be halved.
他们缺搭葡萄架的杆儿，没有它们产量会减少一半。
They thanked Tom，without whose support they would not have succeeded.
他们很感激Tom，没有他的支持他们是不会成功的。
特殊结构
“名词/代词+of+which / whom”
It now has 20，000 hectares of land，more than two-thirds of which are under cultivation.
现在它拥有两万公顷土地，其中三分之二之多已经耕种。
Light is the fast thing in the world, the speed of which is 300000 kilometer per second.
光是世界上最快的东西，它的速度是每秒30万千米。
There are 30 chairs in the small hall, most of which are new.
大厅里有三十把椅子，绝大部分是新的。
The textile mill has over 8，000 workers and staff，eighty per cent of whom are women.
这家纺织厂有8千多职工，女职工占百分之八十。
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