Scientists do not know why dinosaurs became extinct, but some theories postulate that changes in geography, climate, and sea levels were responsible. — 科学家们不知道恐龙为何灭绝了，但是一些理论推断这是地理、气候和海平面的变化造成的。 ① dinosaur /ˈdaɪnəsɔːr/ n. 恐龙 ② extinct /ɪkˈstɪŋkt/ a. 灭绝的，不存在的 ③ postulate /ˈpɑːstʃəleɪt/ vt./n. 假定，假设

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Essentially, a theory is an abstract, symbolic representation of what is conceived to be reality.

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Thanks to modern irrigation, crops now grow abundantly in areas where once nothing but cacti and sagebrush could live.

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Anthropologists have discovered that fear, happiness, sadness, and surprise are universally reflected in facial expressions.

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Of the millions who saw Haley’s Comet in 1986, how many people will live long enough to see it return in the twenty-first century.

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The greater the population there is in a locality, the greater the need there is for water, transportation, and disposal of refuse.

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

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The development of mechanical timepieces spurred the search for more accurate sundials with which to regulate them.

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Studies of the gravity field of the Earth indicate that its crust and mantle yield when unusual weight is placed on them.

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Quails typically have short rounded wings that enable them to spring into full flight instantly when disturbed in their hiding places.

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Fungi are important in the process of decay, which returns ingredients to the soil, enhances soil fertility, and decomposes animal debris.

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Most substance contract when they freeze so that the density of a substance’s solid is higher than the density of its liquid.

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By the middle of the twentieth century, painters and sculptors in the United States had begun to exert a great worldwide influence over art.

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Although apparently rigid, bones exhibit a degree of elasticity that enables the skeleton to withstand considerable impact.

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Finally, the coughing reflex in reaction to irritants in the airway produces not a cough during sleep but a cessation of breathing.

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But when consumers do not know they are being lobbied, they may accept claims they would otherwise be suspicious of.

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Buyers and sellers should be aware of new developments in technology which can and does affect marketing activities.

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With modern offices becoming more mechanized, designers are attempting to personalize them with warmer, less severe interiors.

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The worker and soldier castes of termites consist of both males and females, and the queen lives permanently with a male consort.

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Children with parents whose guidance is firm, consistent, and rational are inclined to possess high levels of self-confidence.

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Lucretia Mott’s influence was so significant that she has been credited by some authorities as the originator of feminism in the United States.

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No social crusade aroused Elizabeth Williams’ enthusiasm more than the expansion of educational facilities for immigrants to the United States.

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Since wind-pollinated flowers have no need to attract insects or other animals, they have dispensed with bright petals, nectar, and scent.

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In the absence of a tradition of classical stone-carving and building, the desire to develop Roman amenities would have been difficult to fulfill.

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Out in remote areas of the countryside, in rural locations, music was more traditional; the same songs were enjoyed by previous generations.

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In the second half of the millennium, in the south around the city of Uruk, there was an enormous escalation in the area occupied by permanent settlements.

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By fossils, we mean traces of prehistoric animals such as bones, which become mineralized, or impressions of bones or organs that are left in stone.

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The application of electronic controls made possible by the microprocessor and computer storage have multiplied the uses of the modern typewriter.

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Even though the precise qualities of hero in literary words may vary over time, the basic exemplary function of the hero seems to remain constant.

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

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Many people who wanted to become archaeologists ended up pursuing other careers and contributing to archaeological research only as unpaid amateurs.

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Even before the discovery of germs, beliefs that disease spread by “miasmas” （noxious forms of bad air） prompted attention to sewers and open garbage.

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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.

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With no oceans to dissolve it, outgassed carbon dioxide began to accumulate in the atmosphere, intensifying the greenhouse effect even more.

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Buildings contribute to human life when they provide shelter, enrich space, complement their site, suit the climate, and are economically feasible.

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Research into the dynamics of storms is directed toward improving the ability to predict these events and thus to minimize damage and avoid loss of life.

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Their streamlined bodies, the absence of hind legs, and the presence of a fluke and blowhole cannot disguise their affinities with land dwelling mammals. ① streamline /ˈstriːmlaɪn/ vt. 使成流线型 ② hind /haɪnd/ a. 后面的，在后的 ③ presence /ˈprezns/ n. 存在；出现

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The elimination of inflation would ensure that the amount of money used in repaying a loan would have the same value as the amount of money borrowed.

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Futurism, an early twentieth-century movement in art, rejected all traditions and attempted to glorify contemporary life by emphasizing the machine and motion.

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Acids are chemical compounds that, in water solution, have a sharp taste, a corrosive action on metals, and the ability to turn certain blue vegetable dyes red.

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In other instances, such as the Indus River Valley, the cities lacked a royal precinct and the ostentatious palaces that marked their contemporaries elsewhere.

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Offshore drilling platforms extend the search for oil to the ocean’s continental shelves—those gently sloping submarine regions at the edges of the continents.

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Even those artists who were most dependent on photography became reluctant to admit that they made use of it, in case this compromised their professional standing.

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According to anthropologists, the earliest ancestors of humans that stood upright resembled chimpanzees facially, with sloping foreheads and protruding brows.

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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.

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A rotary engine attached to the steam engine enabled shafts to be turned and machines to be driven, resulting in mills using steam power to spin and weave cotton.

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Self-awareness, even in its earliest stages, might entail an awareness of others, the ability to see their perspective and to look at the world from another’s point of view.

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Various committees acted as an executive branch, implementing policies of the assembly and supervising, for instance, the food and water supplies and public buildings.

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A mountain range may emerge and gradually split a population of organisms that can inhabit only lowland lakes; certain fish populations might become isolated in this way.

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