下列词加es：
1) s/x/ch/sh结尾的词加es
如：class,box,watch,brush,fox,match,dish,glass,
2）“辅音+y”结尾的词,y改为i后,加es
如：city,country,study,
3)下列o结尾的词加es:tomato,potato,hero,zero,mango,negro,...