二、名词作定语的单复数问题
(A)名词作主语,即noun.修饰noun.,前面的名词必须是单数
color effects, employment agenenices, sentence FORM, tree trunks
例外:a sales girl, a sales tax
a greetings card, a sports car
a savings bank, a communications satellite
a systems engineering
(B)man或woman修饰noun.时,其单复数应该同时变
a woman boxer->women boxers, women nurses
(C)表示某一学科的教授、学生、教科书、实验室等教学要素时,只能用学科名本身修饰
a mathematical professor 错
a biological textbook 错
the chemical lab 错
the highest scientific award 错
a mathematical model 对