英语不定冠词,急A horse is a useful animal.这句话中为什么要在useful前加冠词,anima

英语不定冠词,急A horse is a useful animal.这句话中为什么要在useful前加冠词,anima A horse is a useful animal和The horse is a useful animal A cow is a useful animal这句话中的冠词是否错误 ( )horse is ( )useful animal. horses are useful animals/ a horse is a useful animal.马是有用的动 Horses are a useful animal.这句话中的冠词a使用的对吗? an useful animal?还是a useful animal? 为什么useful前有时用a（a useful book）,有时用an（an useful animal）啊 Everyone understands that （） horse is （） useful animal A a;a A horse is a useful animal 两处为什莫都用a 改错：A fox is an useful animal. 1.The dog is a useful animal.