71. People in prehistoric times created paints by grinding materials such as plants and clay into power and then adding water. 史前的人們制造顏料是將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. 黃菊花通常令人生厭，它擠走不那么頑強的植物，并找來很多害蟲。

　　73. Starting around 7000 B.C.，and for the next four thousand years，much of the Northern Hemisphere experienced temperatures warmer than at present. 大約從公元前七千年開始，在四千年當(dāng)中，北半球的溫度比現(xiàn)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. 當(dāng)亨利·福特最初制造汽車為尋求資金支持時，農(nóng)民和一般職員也能擁有汽車的想法被認(rèn)為是可笑的。

　　75. Though once quite large，the population of the bald eagle across North America has drastically declined in the past forty years. 北美禿頭鷹的數(shù)量一度很多，但在近四十年中全北美的禿頭鷹數(shù)量急劇下降。

　　76. The beaver chews down trees to get food and material with which to build its home. 水獺啃倒樹木，以便取食物并獲得造窩的材料。

　　77. Poodles were once used as retrievers in duck hunting，but the American Kennel Club does not consider them sporting dogs because they are now primarily kept as pets. 長卷毛狗曾被用作獵鴨時叼回獵物的獵犬，但是美國Kennel Club卻不承認(rèn)它們?yōu)楂C犬，因為它們現(xiàn)在大多數(shù)作為寵物飼養(yǎng)。

　　78. As a result of what is now know in physics and chemistry，scientists have been able to make important discoveries in biology and medicine. 物理學(xué)和化學(xué)的一個成果是使得科學(xué)家們能在生物學(xué)和醫(yī)學(xué)上獲得重大發(fā)現(xiàn)。

　　79. The practice of making excellent films based on rather obscure novels has been going on so long in the United States as to constitute a tradition. 根據(jù)默默無聞的小說制作優(yōu)秀影片在美國由來已久，已經(jīng)成為傳統(tǒng)。

　　80. Since the consumer considers the best fruit to be that which is the most attractive，the grower must provide products that satisfy the discerning eye. 因為顧客認(rèn)為最好的水果應(yīng)該看起來也是最漂亮的，所以種植者必須提供能滿足挑剔眼光的產(chǎn)品。

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