撇号（apostrophes）
1、表示占有，在单数名词或不定代词后加撇号和s。
Jenny's book
anyone's guess
somebody's laptop
the waltz's tempo
2、表示占有，在复数名词s后加撇号。
my parents' car
the musicians' instruments
3、在人称物主代词后不加撇号。
yours, his, hers, ours, theirs, whose, its
4、用于缩写。
I am = I'm
cannot = can't
they are = they're
I have = I've
let us = let's
you are = you're