2017年10月21日托福阅读机经小范围版

2017年10月21日托福阅读机经小范围版

　　Title：Population Growth in nineteenth-Century Europe

　　阅读原文：

　　Because of industrialization, but also because of a vast increase in agricultural output without which industrialization would have been impossible, Western Europeans by the latter half of the nineteenth century enjoyed higher standards of living and longer, healthier lives than most of the world’s peoples. In Europe as a whole, the population rose from 188 million in 1800 to 400 million in 1900. By 1900, virtually every area of Europe had contributed to the tremendous surge of population, but each major region was at a different stage of demographic change.

　　Improvements in the food supply continued trends that had started in the late seventeenth century. New lands were put under cultivation, while the use of crops of American origin, particularly the potato, continued to expand. Setbacks did occur. Regional agricultural failures were the most common cause of economic recessions until 1850, and they could lead to localized famine as well. A major potato blight (disease) in 1846-1847 led to the deaths of at least one million persons in Ireland and the emigration of another million, and Ireland never recovered the population levels the potato had sustained to that point. Bad grain harvests at the same time led to increased hardship throughout much of Europe.

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　　Title：Poikilotherms

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　　Physiologically, animals can be divided into three groups: homeotherms, which maintain a fairly constant internal temperature regardless of the external temperature; poikilotherms, which have a body temperature that varies according to the surrounding environmental temperature; and heterotherms, which sometimes maintain a fairly constant body temperature and sometimes do not.

　　Poikilotherms, such as amphibians and insects, have a high thermal or heat conductance between the body and the environment, and a low metabolic rate. For this reason body temperature and thus tissue temperature changes with environmental temperature. Being ectothermic and manitaining body temperature by using sources of heat energy such as solar radiation rather than metabolism has advantages. Prisoners of environmental temperatures, poikilotherms of temperate regions, such as snakes, become highly active only when temperature is adequately warm. Because their metabolic ...

　　Title：Comet

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　　Comets are among the most interesting and unpredictable bodies in the solar system. They are made of frozen gases (water vapor, ammonia, methane, carbon dioxide, and carbon monoxide) that hold together small pieces of rocky and metallic materials. Many comets travel in very elongated orbits that carry them far beyond Pluto. These long-period comets take hundreds of thousands of years to complete a single orbit around the Sun. However, a few short-period comets (those having an orbital period of less than 200 years), such as Halley’s Comet, make a regular encounters with the inner solar systemWhen a comet first becomes visible from Earth, it appears very small, but as it approaches the Sun, solar energy begins to vaporize the frozen gases, producing a glowing head called the coma. The size of the coma varies greatly from one comet to another. Extremely rare ones exceed the size of the Sun, but most approximate the size of Jupiter. Within the coma, a small glowing nucleus with a diameter of only a few kilometers can sometimes be detected. As comets approach the Sun, some develop a tail that extends for millions of kilometers. Despite the enormous size of their tails and comas, comets are relatively small members of the solar system.

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　　Title：The Origins of Theater