旅行吧!

1. passengers  2. electricity  3. skyscraper  4. practical  5. express

6. concept  7. Nowadays  8. steam  9. spread  10. limited

11. exit  12. annual  13. installation  14. similarities  15. powerful

16-20  DCADB     21-25  ACBAD

26-30  DBBCA     31-35  BCCBD

36-40  BFCAD     41-45  ABCCD

46. rush hour

47. Up to

48. rather than

49. take part in

50. No one knows where the old man lives or what his name is.

51.  Sometimes taking sleeping pills makes it easier for my mother to fall asleep.