71. People in prehistoric times created paints by grinding materials such as plants and clay into power and then adding water.

　　71.史前的人们制造颜料是将植物和泥土等原料磨成粉末，然后加水。

　　72. Often very annoying weeds, goldenrods crowd out less hardy plants and act as hosts to many insect pests.

　　72.黄色菊花通常令人生厌，它挤走不那么顽强的植物，并找来很多害虫。

　　73. Starting around 7000 B.C., and for the next four thousand years, much of the Northern Hemisphere experienced temperatures warmer than at present.

　　73.大约从公元前七千年开始，在四千年当中，北半球的温度比现在高。

　　74. When Henry Ford first sought financial backing for making cars, the very notion of farmers and clerks owning automobiles was considered ridiculous.

　　74.当亨利.福特最初制造汽车为寻求资金支持时，农民和一般职员也能拥有汽车的想法被认为是可笑的。

　　75. Though once quite large, the population of the bald eagle across North America has drastically declined in the past forty years.

　　75.北美秃头鹰的数量一度很多，但在近四十年中全北美的秃头鹰数量急剧下降。

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