1.可数名词的复数形式要加S There are trees on both sides of the road
2.名词的所有格要加'S 例如 Mary's sister is twelve years old
3.姓氏后面加S表示一家人,例如 THE WHITES 怀特一家人
4.一般现在时,第三人称单数,动词要加S,例如 He plays basketball on every Sunday afternoon.
6.分数词,当分子大于1时,分母要加S,例如 三分之一是 one third,但是三分之二就是 two thirds