who与whom
Who told you the story?（主语）
Who is that man over there?（主语补语）
Whom/ Who did you meet at the airport?（宾语）
Whom did you give the book to?（介词宾语）
whom是who的宾格,在现代英语中一般只用于书面体,在口语中通常用who,但在介词后只能用whom.