taecher,class,mouth,pencil的负数形势

2以s, x, ch, sh结尾的名词后加-es class-classes, box-boxes, watch-watches, dish-dishes 3以-f或-fe结尾的词 变-f和-fe为v再加-es leaf-leaves, thief-thieves, knife-knives, loaf-loaves, wife-wives 加-s belief-beliefs, chief-chiefs, proof-proofs, roof-roofs, gulf-gulfs 4...