who 是做主语成分 后面接动词
如 who did it?
whom 是做宾语成分 动作的对象
如 whom did you give the pen to
如果改成祈使句就很明白
you gave the pen to whom( 宾语）
whose 是 谁的? 后面+名词
whose book is this?
一般回答 my book, his book 什么的