This is a book.里“a”是什么词性?

This is a book This is a book.里“a”是什么词性? Is this a book? Yes,this is. This is s book.(a book提问) this is a book.反问句是Is this a book? This is a book答语 this is a new book 其中的表语是book还是a new book this is a book a book是宾语还是表语?this is a book a book是宾语还是表语?二者怎么区分? This is a book.对a book进行提问 是用this is a book of english 还是用this is a book with english为什么 This is a book 改为复数句 This is a interesting book.找错误! this is a book改为复数形式 This a book is good 怎么改错 Is this a book?的复数句 改错题：This is a my book. This is a book变成一般疑问句 this is a nice book的感叹句?