That's ____(an/a) oid book.是填an吗 为什么呢

That's ____(an/a) oid book.是填an吗 为什么呢 this is an oid car,and that is new car(中间填a或the) Iwant to be a teacher.That's [an] exciting job.为什么填an That's ____ interesting.(a an the /)哪个正确啊? 是a useful book,还是an useful book.为什么?不是所有元音开头的单词前面都加an吗? （1）(a/an) useful book填哪个,为什么?（2）take an active part It is an"u "and that is a "s"中的an和a是否填对? an orange 前为什么是 a 不是 an 呢 The face that she saw was ____ of an old man 为什么填THAT It's such an interesting book.这个句子有错吗?为什么要加an That's an awfully long book to read in a week,but more power 英语 急用a或an填空.5.That's()English book.It isn't a Chinese book.6