15. It’s only by travelling or living in a country and getting to know its inhabitants and their language _________ one can find out _________ a country and its people are like.
________such heavy pollution already, it may now be too late to clean up the river.
John, look at the time,________you play the piano at such a late hour?
—Are you coming to Jeff's party? —I'm not sure. I________go to the concert instead.
Mr. Bush is on time for everything. How________it be that he was late for the opening ceremony?
Tom, you________leave all your clothes on the floor like this!