我是个英语菜鸟,请问8-year-old前面是用a还是an呢/

我是个英语菜鸟,请问8-year-old前面是用a还是an呢/ one-year-old boy 前面是填a还是an呢? one－year-old前面用an还是a 是a eight-year-old 还是an eight-year-old she is an 8-year-old girl 和she is a 8-year-old girl 到底前面是an 18—year—old前面用a还是用an 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 请问是an eleven-year-old boy还是an eleven-year old 请问是six-year-old还是six years old还是six-years-old?(这个空签名有个a ) an onehundred-year-old man用a还是an 英语问题an还是a eight-year-old boy