定语从句中介词加关系副词的用法.比如from where

“介词+关系词”的用法
1、关系代词在从句中作介词的宾语时，介词常可以提前，但介词提前时，关系代词只能用which 或 whom。
如：The school (that/which) he once studied in is very famous.
→The school in which he once studied is very famous.
Tomorrow I will bring here a magazine (that/which) you asked for.
→Tomorrow I will bring here a magazine for which you asked.
We'll go to hear the famous singer (whom/that/who) we have often talked about.
→We'll go to hear the famous singer about whom we have often talked.
2、关系副词when, where, why 和介词+which之间的关系。
关系副词when, where, why可以用适当的介词+which来替代。介词的位置非常灵活，有时放在关系代词之前，有时放在动词之后。如：when=in/on/at…+which,    where=in/on/at…+which,    why=for+which
如：I won’t forget the date when( on which) I was born.
This is the room where (in which) I lived. = This is the room which I lived in.
I don’t know the reason why (for which) he hasn’t come today.
Tom still remembers the days when (in which) they lived in Tianjin.
 注意：
1). 含有介词的动词短语一般不拆开使用，如：look for, look after, take care of等
如：This is the watch which/that I am looking for. (√)      This is the watch for which I am looking. (F)
2). 若介词放在关系代词前，关系代词指人时用whom，不可用who或者that；指物时用which，不能用that；关系代词是所有格时用whose
如：The man with whom you talked is my friend. (√)       The man who/that you talked with is my friend. (F)
The plane in which we flew to Canada is very comfortable. (√)
The plane in that we flew in to Canada is very comfortable. (F)
3).“介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词或者数词
如：He loved his parents deeply, both of whom are very kind to him.
      In the basket there are quite many apples, some of which have gone bad.
There are forty students in our class in all, most of whom are from big cities.
4). 把握“介词＋关系代词”结构中介词的选用
介词的选择与主句中先行词的搭配密切相关。
如：That”s the reason for which he was late for school.      This is the book on which I spent 8 Yuan.
介词选择的三大规则：
1.       取决于从句中的谓语动词同介词的搭配。（V+ pre.）
如：He is the man whom I talked with this morning.
2.       取决于先行词同介词的常规搭配。
四组常考的搭配：1）extent degree （程度）
同 to 搭配
2）price(具体多少钱时与at; 若指价格方面与in 搭配) speed rate
同at搭配
3）field area aspect sphere （领域，方面）
同 in 搭配
例句：The field in which I studied in university is psychology.
4) basis ground foundation （基础）同on 搭配

这个很简单，定语从句中，有介词的时候就用where 不用死扣语法

在北师大版高一新教材第3模块第7单元第1课课文中有这样的一句：He was blown off course and found himself in an unkown land,from where he eventually reached Greenland.
这里的where指的是in an land而不是land,因此只能用关系副词,而不用from which.再如：
He stood under the tree,from where he could see his son swimming.
You can go across the river,from where you can take a boat.