21. In my opinion, nuclear power is not only expensive but also to our environment. A. danger B. dangerous C. rick D. disaster 22. With teleportation, you disappear at a place, and then in another place seconds later. A. appears B. appeared C. reappear D. reappears 23. Every day over 1,000 new cars add to the city and the city of over 20 million people is getting more and more . A. expensive B. famous C. difficult D. gridlocked 24. My brother and I often come to school foot. A. at B. in C. by D. on 25. Skycycling tubes will be easy . A. drive B. to drive C. ride D. to ride 26. The white cat is Helen’s, and the black cat is . A. my B. I C. mine D. of mine 27. Driverless cars have already , and they look so cool. A. gone B. travelled C. exist D. existed 28. This is Linda’s hat, and those shoes are . A. her B. hers C. our D. their 29. If I have a jet pack. I will use to fly anywhere easily. A. my B. mine C. his D. their 30. A sky safety system can help cars to traffic jams and crashes. A. prevent B. have C. use D. take 31. I think in the future cities will be more crowded and the traffic will get . A. good B. well C. worse D. worst