an American boy 为什么冠词用an?

an American boy 为什么冠词用an? ----American boy (a/an/the) She is an American .这里加不加冠词?American 大写否? I am an America(n) boy.用America还是American? Jim am an American boy.什么意思? Jim is an" "(Americe\American)boy. As an American boy,Jack can_______Chinese. Tom is an American boy.(变为一般疑问句）— —an American boy? 用a an 冠词的易错词 如an amazing girl an honest boy a university 等词 Jack is English.He is an English boy.为什么第一个English不用冠词? an 8-month-old boy为什么用an? 用 a American 还是 an American