1-3 BAC

4-7 DCAD

8-11 ABDC

12-15 ADAB

16. B 17. A 18. G 19. F 20. D

21. D 22. A 23. C 24. A 25. D

26. D 27. B 28. A 29. C 30. C

31. B 32. D 33. B 34. A 35. D

36. D 37. C 38. A 39. C 40. B

41. was built 42. in 43. to walk 44. spending 45. better

46. hired 47. but 48. the 49. watchtowers 50. daily

短文改錯：

1.are→is

2.go后加to

3.friend→friends

4.刪除turn后的out

5.little→few

6.our→their

7.talk→talking

8.kept→keep

9.where→when/whenever

10.mostly→most