eleven前是a还是an

eleven前是a还是an a eleven-year-old还是an eleven-year-old 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 请问是an eleven-year-old boy还是an eleven-year old eleven和effect前面冠词用a还是an uniform前+a还是an unifrom前用什么介词,是an 还是a? one 前的冠词是a 还是an? 我们都知道是an unbrella那如果单单字母U前用a还是an? onion前用介词a还是an mp3前用冠词a还是an MP4前加a还是an不定冠词 University前用不定冠词a还是an? MP4前加an,a还是the exciting前加a还是an hour前用a还是用an 单词 uncle前加a还是an Australian前用a还是an