Although he is only a boy. He knows a lot.A. five year oldB. five-year-oldC. five-years-o

问题补充：

Although he is only a boy. He knows a lot.

A. five year old

B. five-year-old

C. five-years-old

D. five-year-olds

答案：

A. five year old

(答案→)B. five-year-old

C. five-years-old

D. five-year-olds

解析：

试题分析:根据语境和选择项的提示可知此句的含义是虽然他只有五岁，但是他知道的很多。此题考查的是合成形容词的基本构成。根据语法知识可知选择C。