问题补充：
—That must have been a lot of work.
—Yeah, it us three days to finish it.
A. takes
B. had taken
C. took
D. was taking
答案：
A. takes
B. had taken
(答案→)C. took
D. was taking
解析：句意：那肯定有很多工作要做。是的，完成它花费了我们三天的时间。must have been表示对过去的肯定推测，可知事情发生在过去，现在已经完成了，动作不再持续，只表示过去的某个动作，故选C
