an onehundred-year-old man用a还是an

an onehundred-year-old man用a还是an 是a eight-year-old 还是an eight-year-old one－year-old前面用an还是a 是a old man还是an old man?如果是an的话,那为什么university是用a呢? Mr Wang is an man.A.28-year-old B.80-year-old 为什么 英语问题an还是a eight-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. a man还是an man? “an old man ” 为什么用“an” 18—year—old前面用a还是用an 我是个英语菜鸟,请问8-year-old前面是用a还是an呢/