This is__ useful dictionary.填a还是an呢?

This is__ useful dictionary.填a还是an呢? A dictionary is an useful book.找错 This is ___ useful dictionary .选择：A.an B.a C.the D./ 填冠词.2.This is a useful dictionary,I think.So it is,and it's( 1.i have _________ useful dictionary.是用a 还是an? an useful animal?还是a useful animal? an ufesul还是a useful useful前是加a还是an useful one前用an还是a useful前用a还是用an an useful book还是a usefull book? useful前面用an还是a?为什么?