对定语从句的不解之处书上说：介词+关系代词的定语从句可以有from where,since when比如：She loo

对定语从句的不解之处
书上说：介词+关系代词的定语从句可以有from where,since when
比如：She looked out of the window ,from where she could see the whole street.书中这里用了from where 却不用from which
还有,she wrote this book in 1949,since when China began to be stronger and stronger,这里不用which
但是我很疑惑
from since都是介词,后面应该加名词,你或许会告诉我,where和 when都可以作为关系代词（代名词）用,这个我知道,但是书中还有一例
I remember the days on ____which____ I joined the League
或I remember the days during which I joined the League
这样,问题就出现了分歧,这里用了which ,那为什么就不用when 了呢
还有the town is beautiful,in which I used to live
这里怎么就不用where 了呢
还有,we got the party ar 7,by which time they had left
这里又能否用by when 呢
因此现在的问题就是,since from等后面的关系代词是墨守成规确定的,还是需要结合句子考虑的

简单地说,是应该固定记住from where和since when的固定搭配.
不过,我觉得你更应该了解的是which对应的原独立句成分是it,或that/this等等一切宾语成分.where对应的是地点状语there.when对应的是时间状语then(表示“那个时候”的then,不是表示“然后”的then).所以回到你所有的句子,一看都是清楚明白的：
1.She looked out of the window ,from where she could see the whole street.回到独立小句：She looked out of the window.She could see the whole street from there【the window】.如果你觉得可以说she could see the whole street from it.那绝对是你基础有问题,所以会导致现在定语从句出错.
2.she wrote this book in 1949,since when China began to be stronger and stronger.==> she wrote this book in 1949.Since then【那个时候,指1949】 China began to be stronger and stronger.同理,为什么不能用which?因为which对应的原独立句成分是it.假如可以用which,就意味着原独立句可以说since it China began to be stronger and stronger,事实上那是绝对不可能的.
其他介词后面做宾语的关系代词,就只有which能胜任了.
3.I remember the days on ____which____ I joined the League 这个句子只能用which,简单地说是因为有 on .回到独立小句,是I remember the days.I joined the League on these days.作为on 的宾语these days,只有which能指代,你不可能说I joined the League on when的.只能说I joined the League then.所以,想用when吗?可以,删掉on,变I remember the days 【when】I joined the League.
同理
4.the town is beautiful,in which I used to live.因为要做in的宾语,只能是which.回到独立小句,相当于the town is beautiful.I used to live in the town.作为in 的宾语the town,只有which能指代,你不可能说I used to live in there的.只能说 I used to live there.所以,实在想用where?可以,拿走in ,变the town is beautiful,where I used to live.但实际上这里where不能引导用逗号隔开的非限定性定语从句,所以句子还是不对,但换成下面这种句子就没问题：I'll never forget the beautiful town where I used to live.