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。

　　76. The beaver chews down trees to get food and material with which to build its home.

　　76.水獭啃倒树木，以便取食物并获得造窝的材料。

　　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.

　　77.长卷毛狗曾被用作猎鸭时叼回猎物的猎犬，但是美国Kennel Club却不承认它们为猎犬，因为它们现在大多数作为宠物饲养。

　　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.

　　78.物理学和化学的一个成果是使得科学家们能在生物学和医学上获得重大发现。

　　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.

　　79.根据默默无闻的小说制作优秀影片在美国由来已久，已经成为传统。

　　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.

　　80.因为顾客认为最好的水果应该看起来也是最漂亮的，所以种植者必须提供能满足挑剔眼光的产品。

　　81. Television the most pervasive and persuasive of modern technologies, marked by rapid change and growth, is moving into a new era, an era of extraordinary sophistication and versatility, which promises to reshape our lives and our world.

　　81.电视，这项从迅速变化和成长为标志的最普及和最有影响力的现代技术，正在步入一个新时代，一个极为成熟和多样化的时代，这将重塑我们的生活和世界。

　　82. Television is more than just an electronics; it is a means of expression, as well as a vehicle for communication, and as such becomes a powerful tool for reaching other human beings.

　　82.电视不仅仅是一件电器；它是表达的手段和交流的载体并因此成为联系他人的有力工具。

　　83. Even more shocking is the fact that the number and rate of imprisonment have more than doubled over the past twenty years, and recidivism------that is the rate for re-arrest------is more than 60 percent.

　　83.更让人吃惊的事实是监禁的数目和比例在过去的二十年中翻了一番还有余，以及累犯率——即再次拘押的比例——为百分之六十强。

　　84. His teaching began at the Massachusetts Institute of Technology, but William Rainey Harper lured him to the new university of Chicago, where he remained officially for exactly a generation and where his students in advanced composition found him terrifyingly frigid in the classroom but sympathetic and understanding in their personal conferences.

　　84.他的教书生涯始于麻省理工学院，但是William Rainey Harper把他吸引到了新成立的芝加哥大学。他在那里正式任职长达整整一代人的时间。他的高级作文课上的学生觉得他在课上古板得可怕，但私下交流却富有同情和理解。