13-year-old=13 years 如果是,区别在哪?

题目

13-year-old=13 years 如果是,区别在哪?
tina is a ______ girl
A 13-year-old B13 years old

答案

答案是A.
13-year-old,只能做定语.
13 years old,只能做表语,例如Tina is 13 years old.