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：grownup→grownups, brotherinlaw→brothersinlaw, standby→standsby.

　　9)复合形容词做定语时，其中的名词保持单数：a sixyearold boy，a twohundredpage 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) fiftyminutes

　　C) fiftyminute

　　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。