改错：A fox is an useful animal.

改错：A fox is an useful animal. an useful animal?还是a useful animal? ___ elephant is ___ useful animal.A.An;an B.An;a C.Thn;an D. The elephant is _____ useful animal to human beings.A.a B.an 1.The dog is a useful animal. the internet is an useful英语改错 A horse is a useful animal和The horse is a useful animal ( )horse is ( )useful animal. an eiephant is-useful animal的横线应填什么?A.a B.an C.the D./ The hourse is a useful animal.Horses are useful animal都是马是有用 为什么useful前有时用a（a useful book）,有时用an（an useful animal）啊 a horse is an animal