【2012重庆卷】It was 80 years before Christopher Columbus crossed the Atlantic______ Zheng sailed to East Africa
--- Are you going to attend Jay Chou Concert in Suqian this weekend?--- ______. It’s too good a chance to miss. I’m his die-hard fan.
--- Who ______ it be that is singing in the next room?--- It _______ be Lucy, but I am not sure.
Not until World War II ______ to use new chemical techniques to purify penicillin.
--- What did the manager say at yesterday’s meeting?--- So you______ to him carefully.
--- Did Jack come back early last night?--- Yes. It was not yet eight o’clock ______ he arrived home.