A:During the summer months, several thousand people visit the park a day which is known for its waterfalls and rock formations.

B:During the summer months, several thousand people a day visit the park which is known for its waterfalls and rock formations.

1.为什么a day 不算频度状语，修饰visit？

2.为什么B句要优于A句，不是说名词与定语之间可以被状分割吗？

例如Never leave that until tomorrow which you can do today.
3.在B句中a day 算是名词短语，名词短语也能做定语吗？一直只知道介词短语、副词短语、形容词短语、分词短语、不定式短语做定语。

名词短语与名词短语之间是同位语关系，但此处确实只能解释为做定语，还有其他类似的例子吗？