问题
选择题
_____ shouldn’t have part-time jobs because they are too young.
A．Thirteen years old
B．Thirteen-year-old
C．Thirteen-year-olds
D．Thirteen year olds
答案
答案：C
此题重点考查合成形容词的基本构成，数词+名词(+形容词)；合成形容词中的名词(year, hour, metre, month等)必须用单数形式。