31. All his attention______on the computer game, so he even didn't notice his mother enter the room.

24. I was spending my holidays at the time, so I have no idea how it________

35. —Did you attend David’s wedding last night?
—No. I ________ before that.

Great changes ________ in the city since 1979.

15. An awful crash between an express train and a bus _____ , however, occur the other day in Russia.
A. does    B. did     D. has to     D. had to

4. People begin to know that most environmental problems exist because necessary  measures for preventing them _______taken in the past.

16．After driving for 20 miles, Jackson realized that he______in the wrong direction.

12．In only 10 years, our province has been___into an advanced industrial province.

35. Many people agree that never in history    a more splendid opening ceremony than that of the Beijing Olympics.

26. Since the beginning of the vacation, I    across the country, and my next stop is the Wuyi Mountains.