当主语是第一人称(I,We)、第二人称(You)或者是第三人称复数(They,students,teachers.)时，often后面的动词不加-s；当主语是第三人称单数(She,He,It,人名.)时，often后面动词加-s。
双语例句
1、Pupils often play games in the playground during breaks.
课间休息的时候，小学生们常在操场上做游戏。
2、As they often play football together, they have got to know each other quite well.
他们常在一起踢足球，一来二去地也就熟了。
3、They often play table tennis together.
他们常在一搭打乒乓球。
4、We often play cards.
我们时常玩牌。
5、Growing up alone, they often play by themselves.
他们独自一人长大，经常自己一个人玩。