英语名词变复数的规则：
1、直接加-s.
如： tree-trees树, desk-desks桌 card-cards, parent-parents,
2、以s,x, ch, sh 结尾的加es.
如：bus-buses, box-boxes, watch-watches 手表, brush-brushes 刷子, glass-glasses.
3、以辅音字母+ y结尾的，改y为i再加es.
如：country-countries 国家、乡村, city-cities 城市, baby-babies, family-families,
特例：：boy-boys, monkey-monkeys, toy-toys, play-plays(剧本)
4、以f或者fe 结尾的词，改f为v,再加es.
如：knife-knives刀, leaf-leaves 树叶, wife 妻子-wives.