fifteen-year-old 和fifteen years old 有什么区别?包括他们各自的用法

fifteen-year-old 和fifteen years old 有什么区别?包括他们各自的用法 fifteen-years-old的用法与区别 英语问题a fifteen-year-old与a fifteen-years-old等到底有什么区别呢?我一直都没搞懂, fifteen-year-olds和a fifteen-year-old boy years old 和year-old的区别和用法 five-year=old和five years old用法有什么区别啊 six-year-old和six years old用法有什么区别? 11-year-old和11 years old有什么区别 three-year-old 和 three years old 有什么区别 three -year-old 和 three years old有什么区别? 变一变 She is fifteen years old （对画线部分提问,画线的是fifteen years old year-old和years old的区别