1. 单复数同形。Crossroads, deer, sheep, means, series, species, Chinese, Swiss.
2. 只变内部元音字母。 Foot, man, woman, tooth, goose, mouse.
4. 外来词的特殊变化,um变为a,sis变为ses。analysis, bacterium, basis, crisis, datum, medium, phenomenon, thesis.
5. 复合名词
5.1. 主体名词之后加s。eg. son-in-law女婿,变为sons-in-law
5.2. 若无主题名词,则在词尾加s。eg. grown-up成年人,变为grown-ups.
5.3. 由man或者woman结尾的名词,只把词尾的man变为men,woman变为women。eg. policeman变为policemen
5.4. 由man和woman修饰的名词短语,既要变为men和women,还要把其所修饰的名词变为复数。eg.a woman teacher变为 two women teachers.
6. 用汉语拼音表示的名词,无复数形式。eg. yuan后面永远不加s。