must have been completed表过去发生的动作

有读者问这样一道选择题：

The construction of our library_________by the end of next week.

A. must have been completed

B. must complete

C. must be completed

D. must have completed

答案是C，可我觉得A更对，您看呢？

答案是对的。A不对，因为它只可表推测过去，如把句中的next week改作last week(month，year)，就对了。