问题补充：
Mike is boy.
A. one 11-years-old
B. one 11-years old
C. one-11-year-old
D. an 11-year-old
答案：
A. one 11-years-old
B. one 11-years old
C. one-11-year-old
(答案→)D. an 11-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:麦克是一个十一岁的男生. 结合语境可知本句合成词用作形容词,故选D.
