— It is reported that America offered to help us build aircraft carriers. — But many citizens would rather our country __________ one by ourselves.

 He insisted the person referred ______ put into prison at once.

If  we ___________some measures, we might have prevented the environmental pollution．

One ought _____ for what one hasn’t done.

–Where are the students? How could they keep us waiting for so long? –They started an hour ago and they ____ be here in fifteen minutes, I think.