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
网友回答
A. Thirteen years old
B. Thirteen-year-old
(答案→)C. Thirteen-year-olds
D. Thirteen year olds
解析：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。