仔细阅读：

　　46. B) They formulated a dress code with distinctive American features.

　　47. D) It was a completely new invention.

　　48. C) Ease of care

　　49. A) A shift of emphasis from beauty to utility.

　　50. C) They advocated equity between men and women.

　　51. D)They have changed the previous migration habits of certain birds.

　　52. D)They are more likely to be at risk of dying

　　53. B)They may eat something harmful.

　　54. C)They are not attracted to the rubbish dumps on their migration routes.

　　55. A)The potential harm to the ecosystem.