an 8-year-old 为什么加an而不是a,是不是8是元音开头的?

an 8-year-old 为什么加an而不是a,是不是8是元音开头的? an eight-year-old一定要加an吗? _____(a/an)1-year-old boy _____(a/an)8-year-old boy _____(a/an)11-year-old boy_____(a/an)13-year-old boy an eleven year old 和 an eleven-year-old用哪个?为什么 a one-year-old boy为什么不是an Mr Wang is an man.A.28-year-old B.80-year-old 为什么 Lily,_______girl,is very popular in our class.A、a 8-year-old B、a 8 year old C、 an 8-year-old D、an 8-years-old He is an 8-year-old boy.对 8-year-old画线提问 英语翻译She is a 8-year-old girl还是She is an 8-year-old girl. a eleven-year-old还是an eleven-year-old 是a eight-year-old 还是an eight-year-old 请问是he only has an 8-year-old son还是he has only an 8-year-old son? an eight-year-old boy为什么year不加s 这属于什么语法可是把连字符去掉吧years加上s也不对啊 an eight years old boy 是错的 新概念英语2册56课问题1.once a year,a race is held for old cars.请问能否把a去掉改成：once a year,race is held for old cars.为什么?2.old car race is held ones a year.请问能否加个an改成：an old car race is held ones a year Mary is( )girl.A.an 8 year old B.8 years old C.the 8 years old D.an 8-year-old选择 Lily is ____ girl.A.a 8-years-old B.an 8-year-old C.an 8-years-old D.a 8-year-old an 8-month-old boy为什么用an? 8.Kate is an eight-years-old boy.这里为什么year还要加s,不是有横线就不用加吗?还有什么特殊情况?