Li Lida a____boy crossed the Qiongzhou Channel in June 2000.选择什么?为什么?a.thirteen-year-old b.thirteen-years-oldc.thirteen years oldd.thirteen-years old

Li Lida a____boy crossed the Qiongzhou Channel in June 2000.选择什么?为什么?a.thirteen-year-old b.thirteen-years-oldc.thirteen years oldd.thirteen-years old
Li Lida a____boy crossed the Qiongzhou Channel in June 2000.选择什么?为什么?
a.thirteen-year-old
b.thirteen-years-old
c.thirteen years old
d.thirteen-years old

Li Lida a____boy crossed the Qiongzhou Channel in June 2000.选择什么?为什么?a.thirteen-year-old b.thirteen-years-oldc.thirteen years oldd.thirteen-years old
答案选a
解析：“基数词-year-old” 一般用来做定语修饰名词.
例如： 一个13岁的男孩：a thirteen-year-old boy
She was an eight-year-old girl that year.
而基数词+years old,常放在be动词后作表语.Anna is only five years old.

A,英文中一种词组变形容词的形式