18—year—old前面用a还是用an

18—year—old前面用a还是用an one－year-old前面用an还是a three-year-old boy 这样的前面用a还是an?两种我都看过.. year前面用a 还是用an （a/an）18-year-old 18前面是an还是a an onehundred-year-old man用a还是an 当an eleven-year-old girl中eleven是数字11时用a还是an当an eleven-year-old girl中eleven是数字11时前面用a还是an a eleven-year-old还是an eleven-year-old 是a eight-year-old 还是an eight-year-old one-year-old boy 前面是填a还是an呢? 一个18岁男孩 用英语怎么说（要用连字符）请问是 an eighteen-year-old boy 还是 a eighteen-year-old 为什么? she is an 8-year-old girl 和she is a 8-year-old girl 到底前面是an 还是a 请总结一下用an 和a 来修饰的名词 比如 是an 18-year-old girl 还是用a 什么的 谢谢哈 3.Liu Ming is_____18-year-old student.He got a gold medal in the competition.A.a B.an C.the D./像这种：num.-year-old的结构,前面的不定冠词用什么?用的依据是什么? 是a one-year-old boy还是an one-year-old boy a 11-year-old boy还是an 11-year-old boy 英语翻译She is a 8-year-old girl还是She is an 8-year-old girl. 一年用英语怎么说应该是an year 还是 A year?