an useful animal?还是a useful animal?

an useful animal?还是a useful animal? an animal还是a animal说明为什么? an animal doctor还是a animal doctor 改错：A fox is an useful animal.同题 useful前是加a还是an an ufesul还是a useful 为什么useful前有时用a（a useful book）,有时用an（an useful animal）啊 ___ elephant is ___ useful animal.A.An;an B.An;a C.Thn;an D.A;an___ elephant is ___ useful animal.A.An;an B.An;a C.Thn;an D.A;an答案给的是B,为什么不能第一个空不能填The?还有到如何判断u开头的字母到底是an还是a? ( )elephant is ( )useful animal to p( )elephant is ( )useful animal to peopleA an,a B an,the C the,an D /,an回答时请适量说明原因 _______horse is a useful animal . an useful book还是a usefull book? useful one前用an还是a useful前面用an还是a?为什么? A horse is ( ) useful animal.A.an B.a C.the D.this The elephant is _____ useful animal to human beings.A.a B.an C.the D./ ( )horse is ( )useful animal.A.The;an B.The;the C.A;a D.A;an选什么?为什么? A house is a useful animal 翻译 是an useful book还是a useful book 加a 或者an 主要看什么