there Now Here 是不是指示代词

there, now, here在这里是副词，他们在句首，并且主语是非人称代词时，一般需要倒装。是为了表示强调。
这三个句子的主语其实分别是：a bookstore, twenty books,your turn.所以动词分别是：stands, happens, comes.
正常语序应该是：
A bookstire stands there.
Twenty books happens to be left there.
Your turn comes now.
The bus comes here.