21.—It is raining cats and dogs.
22.　—　　　..
23.

17..In the United States, bus travel doesn't cost much as train travel, 　　?
18.

2. ______was known to them all that William had broken his promise______ he would give each of them a gift.

31. Last week, only two people came to look at the house, ____ wanted to buy it.

15. Not until father came in ______ to prepare my lessons.

34. The space is left to let the rail expand when it gets hot, ______?

32. Only when he failed ______ the stress he was under.

29. Realizing ______ I had been able to accomplish, my fears of failure grew rapidly.

35. I think I can fix the car on Wednesday.  ______, you’ll have to wait till Friday.

31. ______ is no doubt that the media play a major role in influencing people’s opinions.

A．This

B．That

C．What

D．There