1.在大多数名词末加“'s”
the boy's toy, men's work
2.以s结尾的复数名词直接加“'”
the students' reading room
3.以s结尾的单数名词加“'”
Dickens' novels the actress' performance
4.合成名词在最后一个词上加“s”
her brother-in-law's piano.
Somebody else's books. （重要！）
重点：除用于有生命的人外，“'s”格还可用于度量衡、地域、天体及一些习语中：
an hour's drive, a mile's journey
ten pounds' weight. Beijing's weather
the earth's surface
a stone's throw 投石之距离
at one's wits end 智穷计尽
to one's heart's content 尽情地
by a hair's breadth 千钧一发
at a snail's pace 缓慢地
5.双重所有格：
如果被修饰的名词前有不定冠词、不定代词、指示代词、疑问代词修饰。则要采用双重所有格。
a friend of mine （名词性物主代词）
a child of hers
the love poems of your sister's
注意区别：
a portrait of her mother 她母亲的画像（画中人）
a portrait of her mother's 她母亲拥有的画像中的一幅（不一定是她母亲的画像）
