Next time__you come in,please close the doora.when b.\ c.that d.at which为什么不选B?

Next time__you come in,please close the doora.when b.\ c.that d.at which为什么不选B?
Next time__you come in,please close the door
a.when b.\ c.that d.at which
为什么不选B?

Next time__you come in,please close the doora.when b.\ c.that d.at which为什么不选B?
个人觉得是答案错,应该选B.next time直接可以做时间状语的连词,类似each time,the first time等等.

答案是D??
我看是A

答案是错的吧，
Next time__you come in,please close the door
应该选择A项吧。这里没有具体时间出现啊，怎么会用at which?