—Where is Bob? I cannot find him anywhere.—He have been off long. I heard him make a call just now.
This is such a difficult question ______ none of us can answer.
Everyone in the class is expected to ______ these discussions.
— Does your brother intend to learn German? —Yes, he intends _______.
We must do whatever we can ______ those who are in trouble.
—Have you handed in your schoolwork yet? —Yes, I have. I guess it ______ now.