50. The ancient Hopewell people of North America probably cultivated corn and other crops, but hunting and gathering were still of critical importance in their economy.

50.北美远古的Hopewell人很可能种植了玉米和其他农作物，但打猎和采集对他们的经济贸易仍是至关重要的。

51. Using many symbols makes it possible to put a large amount of information on a single map.

51.使用多种多样的符号可以在一张地图里放进大量的信息。

52. Anarchism is a term describing a cluster of doctrines and attitudes whose principal uniting feature is the belief that government is both harmful and unnecessary.

52.无政府主义这个词描述的是一堆理论和态度，它们的主要共同点在于相信政府是有害的，没有必要的。

53. Probably no man had more effect on the daily lives of most people in the Untied States than did Henry Ford a pioneer in automobile production.

53.恐怕没有谁对大多数美国人的日常生活影响能超过汽车生产的先驱亨利.福特。

54. The use of well-chosen nonsense words makes possible the testing of many basic hypotheses in the field of language learning.

54.使用精心挑选的无意义词汇，可以检验语言学科里许多基本的假定。

55. The history of painting is a fascinating chain of events that probably began with the very first pictures ever made.

55.优化历史是由一连串的迷人事件组成，其源头大概可以上溯到最早的图画。

56. Perfectly matched pearls, strung into a necklace, bring a far higher price than the same pearls told individually.

56.相互般配的珍珠，串成一条项链，就能卖到比单独售出好得多的价钱。