48. He bought the bike two years ago.(改为同义句) 

He the bike for two years.

47. The students talked happily. At that time Mr. Green came in.(合并成一个句子) 

The students was happily Mr.Green came in.

46. The bus has arrived here. It arrived ten minutes ago.(合并成一个句子) 

The bus here ten minutes.

45. The Green family moved to France two years ago.(改为同义句)

 two years the Green family moved to France.

44. Her mother has been a Party member for three years.(改为同义句) 

Her mother the Party three years ago.

43. Miss Gao left an hour ago.(改为同义句) 

Miss Gao  foranhour.

42. This factory opened twenty years ago.(改为同义句) 

This factory  for twenty years.

41 . He died last year.(改为同义句) 

He  for a year.

40. They have been here since 2000.(对画线部分提问)

 have they been here?

39. Those words tell people how they can use the machine.(改为简单句) 

Those words tell people how the machine.