taecher,class,mouth,pencil的负数形势

teachers
classes
mouths
pencils

II. 名词的数：
1. 规则名词的复数形式：
名词的复数形式，一般在单数形式后面加-s或-es。现将构成方法与读音规则列表如下：
规则 例词
1一般情况在词尾加-s
map-maps, sea-seas, girl-girls, day-days
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以辅音字母加y结尾的名词，变y为i加-es
party-parties, family-families, story-stories, city-cities
5以元音字母加y结尾的名词，或专有名词以y结尾的，加-s
toy-toys, boy-boys, day-days, ray-rays, Henry-Henrys
6以辅音字母加-o结尾的名词
一般加-es
hero-heroes, Negro-Negroes, potato-potatoes, tomato-tomatoes

不少外来词加-s
piano-pianos, photo-photos, auto-autos, kilo-kilos, solo-solos

两者皆可
zero-zeros/zeroes, volcano-volcanoes/ volcanos
7以元音字母加-o结尾的名词加-s
radio-radios, bamboo-bamboos, zoo-zoos