—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

春天梅花绽放的时候，距离梅花很远的地方就能闻到花的香味，这种现象说明了_________________ ；夏天，雨后天晴，池塘里荷叶上的水珠随荷叶拂动而滚动不止，当两滴滚动的水珠相遇时，会汇合变成一滴较大的水滴，这说明：___________________________。