1)单数名词加s: students, apples, bags, trees, books, brothers.
2)以s、x、sh、ch结尾的名词加es: glasses, boxes, brushes, matches.
3)以辅音字母加y结尾的名词，变y为i加es: cities, babies, enemies.4)以f或fe结尾的名词，多数变f为v加es: wives, knives.但有些词只加s: roofs, proof s, chiefs.
5)以o结尾的名词，有些加es: Negroes, heroes, tomatoes, potatoes.其它加s: radio s, zoos, pianos, photos.
6)不规则名词：foot→feet, goose→geese, tooth→teeth, child→children, man→me n, woman→women, sheep→sheep, deer→deer, mouse→mice.
7)某些外来词变复数：datum→data, medium→media, bacterium→bacteria, curriculum→curricula, criterion→criteria, phenomenon→phenomena. (um/on→a)analysis→analyses, basis→bases, crisis→crises, diagnosis→diagnoses.(is→es )
8)复合名词变复数：以不可数名词结尾的复合名词无复数形式，如：homework.
以man或woman为前缀的复合名词变复数，前后两个名词都变复数，如：manservant→menservants, woman student women students.
其它复合名词变复数：grownup→grownups, brotherinlaw→brothersinlaw, standby→standsby.
9)复合形容词做定语时，其中的名词保持单数：a sixyearold boy，a twohundredpage book
【例句】A second doctor must confirm that these criteria ______ and the death must be re ported to the police department.
A) has been met
B) have been met
C) was met
D) was being met
criteria是复数形式，故A，C，D都为错误选项。正确答案为B。
1) The university authorities are seriously considering abandoning the traditional______class.
A) fifth minutes
B) fiftyminutes
C) fiftyminute
D) fifty minute s
复合形容词用作定语时，其中的名词不变复数，故B不对。A不能做定语，D应为fifty minutes ，正确答案为C。