A;Do you know when he will come back?B;----(A,Till a week B.Not until next week)

肯定选B的

问题问的是时间点，回答也应该是时间点。

A;----Do you know when he will come back?
B;----(A,Till a week B.Not until next week)

选B.
其实它是He won't come back until next week.的省略句.

选B
not...until的用法
相当于He won't come back until next week.
他要到下周才回来。

B
A应该写成In a week就对了
He will come back in a week.
或He won't come back until next week.

B
如果选A，意思就成为他一直回一直回，可回来了就是回来了，没回来就是没回来，不可能是延续的，所以排除A

选B是正确的，因为not....until是“直到...才”的意思，因此这句话可写成
He won't come back until next week.