以s,x,z,sh,ch结尾的,加-es,如bus buses,brush brushes;
以辅音字母加y结尾的,变y为i加-es,如city cities,以元音字母加y结尾的,直接加-s,如boy boys;
以辅音字母加o结尾的,加-s,如tomato tomatoes,以元音字母o结尾的,加-s,如radio radios;
以f或fe结尾的,去f或fe加-ves,如thief thieves;
不规则变化的,如child children,man men,foot feet,
单复同形的,如fish fish,sheep sheep。