一个星期有多少天？

How many days ?(这个比较正统、正规)
－－原型:there are seven days in a week.
(或者 How many days does one week have?)
－－原型:A week has seven days.

不用加are there in之类的词，直接译为：

How many days a week?

How many days are there in one week?

How many days does a week has?

How many days are there in a week?

How many days are thete in a week?