He knows it is high time that he ________ at once.

As Commander-in-Chief of the armed forces,I have commanded that all measures               for our defense.

A left-luggage office is a place where bags ______ be left for a short time, especially at a railway station.

Should the present unemployment continue, the society________a more troublesome situation.

——This wall of air is an effective answer to the problem and it ____ work.——But it is a question to put such a wall of air around the statue.