1-3 BAC
4-7 DCAD
8-11 ABDC
12-15 ADAB
16. B17. A18. G19. F20. D
21. D22. A23. C24. A25. D
26. D27. B28. A29. C30. C
31. B32. D33. B34. A35. D
36. D37. C38. A39. C40. B
41. was built42. in43. to walk44. spending45. better
46. hired47. but48. the49. watchtowers50. daily
短文改错：
1.are→is
2.go后加to
3.friend→friends
4.删除turn后的out
5.little→few
6.our→their
7.talk→talking
8.kept→keep
9.where→when/whenever
10.mostly→most
