she knows my name and i know hers为什么给her加s

She knows my name and I know hers.她知道我的名字,我也知道她的名字.
本题考查人称代词的用法.
her是一个形容词性物主代词；hers是名词性物主代词.
hers = her + 名词 例如：
This book is 【her book】.= This book is 【hers】.
My pen is very nice.【Her pen】 is very nice,too.
=My pen is very nice.【Hers】 is very nice,too.