A serious study of physics is impossible ________ some knowledge of mathematics.
—Excuse me. Is this the right way to the Summer Palace? —Sorry, I am not sure, but it ____ be.
They looked at each other, ______.
Mr. Smith, _______ of the ______ speech, started to read a novel.
Look, what a dirty classroom we have got! It really wants ______.
It is high time, I think, that you got down to ______ something in class.