all ready to put it into operation,____________, we’re going to take action as fast as possible.

51. — Who is at the _____ of all thistrouble.— I don’t know.

We were deeply impressed by the schools and teachers________ we had visited there.

How long do you think it will be ______ the Chinese people land on the moon?

Are you _____ the book The Christmas Sweater —Yes, it’s great.