做主语的关系代词在任何情况下都不可以省略
作宾语的关系代词经常被省略,但是若出现“介词+关系代词”时,则关系代词千万不可省略.
例：1.He is a person who I like to talk with.(可填4种）
whom
that
\
2.He is a person with whom I like to talk （这里只能填whom)