—Who______ it be that is knocking at the door?—It ______ be Father, but I’m not sure.
_____ all the inventions have in common is ____ they have succeeded.
One of the orders that we received was that we ______ there on time.
Thank you very much. Without your help, I _______the exams.
We have already placed an order ____ that company _____ the machines.
He is _____ an American as an apple pie.