—Who______ it be that is knocking at the door?—It ______ be Father, but I’m not sure.
It is not easy to learn English well but if you ______, you will succeed in the end.
Water, which seems to be so simple and common, is ______ makes life possible.
William Shakespeare occupied a ______ position in English literature.
We have been told that under no circumstances ______ the telephone in the office for personal affairs.
—Tom is so worried about the test that he said he was going to study all night. —Tell him he should quit ______ and get some help.