It has been announced that candidates ______ remain in their seats until all the papers have been collected. 

——Why did you not come to the party? ——I ______ it, but my car broke down on the way.

It was playing computer games that cost the boy plenty of time that he ______ spent doing his lessons.

------ Who is that man over there? _______ it be our teacher?------ No, it _______ not be our teacher. It _______ be Mr. Zhang.

 Grace doesn't want to move to New York because she thinks if she ________ there，she wouldn't be able to see her parents very often.(2012·安徽)