This January will be very precious for us by which time we ____c

This January will be very precious for us by which time we ____completing the construction work.
A、will finish
B、will have finished
C、have finished
D、will be finished
【正确答案】：B
【题目解析】： 考察英语的时态.by + 表将来时间的短语（比如说by next May ,by the end of this January ,by the end of this month）时,句子谓语动词（表动作）的时态是将来完成时.