52.对　……有影响have an effect on

51.相反　　 in turn

50.消失　 die out

49.靠……过活　 live on

48.掉到地上　 fall on the ground

47.改变平原上的野生动物

change the while wildlife of the plains

46.切掉皮cut off the skins

45.在平原上修建铁路

build railways across the plains

44.用这种种方法　 in this way

43.与土著首领达成协议

make agreements with Native American chiefs