The telephone ______ three times in the last hour, and each time it _____ for my father.
. ______ the ancient Egyptians built the pyramids puzzled people for centuries.
No one but the experts in this field can _____ the difference between them.
—Who______ it be that is knocking at the door? —It ______ be Father, but I’m not sure.
The meeting we had ________ to _______ us finally.
The great _____ of this computer is that it’s so cheap compared to the others.