“How many days are there in a week?”这句话为什么要加“are there”?

“How many days are there in a week?”这句话为什么要加“are there”? How many days are there in a week? How many days there are in a week 造句 How many days there are in a week造句 how many days are there in a week?怎么回答 How many days are there in a week What are they?怎么回答 There are seven days in a week这句话对吗 帮我How many days are there in a weep这句话是什么意思? How many days are there in a week （用英语回答） many,there,are,how,week,a,in,days.）连词成句 How many days are there in a week?的中文意思是什么? how many days are there in a week?的答句是什么