像during, except或者表示分割作用的of等介词通常放在关系代词的前面。如：
★ The years during which he was away were long years to her.
★ He wrote many books, some of which you will read some day.
关系代词who和that用作介词宾语时，介词须置于句末。如：
★ The writer you referred to was an unknown writer.(关系代词who用作介词to的宾语，介词to须位于定语从句之末，who在口语中可以省去)
★ This is the problem that he has been complaining about.(关系代词that用作介词about的宾语，介词about须位于定语从句之末)
有时定语从句中还有其他成分，介词则位于定语从句之中。如：
This is the engineer who he cooperated with in the project.
先行词指人时，关系代词既可以用who, 也可以用that。但关系代词在定语从句中用作主语时，多用主格who。如：
★ Beyond the practical need to make order out of chaos, the rise of the dictionaries is associated with the rise of the English middle class, who were anxious to define and circumscribe the various world to conquer.(persons, those, people等先行词多用关系代词who)
★ It is Tom who should be punished.(在强调结构中，指人时多用who)
★ The American zoologist Donald Griffin, who was largely responsible for the discovery of sonar in bats, coined the term ‘echolocation' to cover both sonar and radar, whether used by animals or by human instruments.
在下列情况中多用that, 而不用who或者which。如：
★ much (很多)
little (很少)
none (没有任何)
everything (任何事情) +先行词 +that
everybody (任何人)
nothing (没有任何)
nobody (没有人)
E.g. There is nothing in the world that can frighten him.
