It’s a pity that you didn’t come to my birthdayparty last night.–I’m terribly sorry. I ________ for an importantlecture.

His money has run out, so he can’t _________ anything else.

The official made the demand that the soldiers ____ atonce _____ battlefront.

The science Festival is an occasion _____ model planes and model rockets are flown over the school grounds.

______ the maths problem is difficult， I’ll try very hard to work it out.