One of the suspects is schoolboy.A. a 18-year-old B. an 18-years-oldC. a 18 years oldD. a

问题补充：

One of the suspects is schoolboy.

A. a 18-year-old

B. an 18-years-old

C. a 18 years old

D. an 18-year-old

答案：

A. a 18-year-old

B. an 18-years-old

C. a 18 years old

(答案→)D. an 18-year-old

解析：英语中两个或多个单词中间可以用短横线连接起来，起一个相当于形容词的作用，这类单词叫做合成词。其一般构成规则就是其构成单词一般都要用原形。句意:嫌疑人之一是一个十八岁的男生。Eighteen的词首音素是元音，故不定冠词用an，选D。