2018年5月19日托福阅读机经
需要考托福的同学对于机经都有一种信任感，那么大家应该如何进行托福机经的学习呢，下面和我一起来看看2018年5月19日托福阅读机经。
天文类Surface Fluids on Venus and Earth
参考阅读：
A fluid is a substance， such as a liquid or gas， in which the component particles （usually molecules） can move past one another. Fluids flow easily and conform to the shape of their containers. The geologic processes related to the movement of fluids on a planet’s surface can completely resurface a planet many times. These processes derive their energy from the Sun and the gravitational forces of the planet itself. As these fluids interact with surface materials， they move particles about or react chemically with them to modify or produce materials. On a solid planet with a hydrosphere and an atmosphere， only a tiny fraction of the planetary mass flows as surface fluids. Yet the movements of these fluids can drastically alter a planet. Consider Venus and Earth， both terrestrial planets with atmosphere.
Venus and Earth are commonly regarded as twin planets but not identical twins. They are about the same size， are composed of roughly the same mix of materials， and may have been comparably endowed at their beginning with carbon dioxide and water. However， the twins evolved differently， largely because of differences in their distance from the Sun. With a significant amount of internal heat， Venus may continue to be geologically active with volcanoes， rifting， and folding. However， it lacks any sign of a hydrologic system （water circulation and distribution）： there are no streams， lakes， oceans， or glaciers. Space probes suggest that Venus may have started with as much water as Earth， but it was unable to keep its water in liquid form. Because Venus receives more heat from the Sun， water released from the interior evaporated and rose to the upper atmosphere where the Sun’s ultraviolet rays broke the molecules apart. Much of the freed hydrogen escaped into space， and Venus lost its water. Without water， Venus became less and less like Earth and kept an atmosphere filled with carbon dioxide. The carbon dioxide acts as a blanket， creating an intense greenhouse effect and driving surface temperatures high enough to melt lead and to prohibit the formation of carbonate minerals. Volcanoes continually vented more carbon dioxide into the atmosphere. On Earth， liquid water removes carbon dioxide from the atmosphere and combines it with calcium， from rock weathering， to form carbonate sedimentary rocks. Without liquid water to remove carbon from the atmosphere， the level of carbon dioxide in the atmosphere of Venus remainshigh.
Origin of the Solar System
Comets
文化艺术类
The Origins of Writing
Live Performance
The Origins of Theater
The Development of Printing
地质类
Early Theories of Continental Drift
Attempts at Determining Earth’s Age
How Soil is Formed
Earth’s Energy Cycle
Thermal Stratification
环境类
The Climate of Japan
The Role of the Ocean in Controlling Climate
经济类
Effects of the Commercial Revolution
Seventeenth-Century European Economic Growth
考古类
Environmental Impact of the Anasazi
The Collapse of the Mays
The Chaco Phenomenon
科学类
The Birth of Photography
Early American Printing Industry
农业类
Agricultural Society in Eighteenth- Century British America
Water Management in Early Agriculture
社会类
Population Growth in Nineteenth-Century Europe
Hunting and the Setting of Inner Eurasia
生物类
Extinctions at the End of the Cretaceous
The Cambrian Explosion
The Extinction of the Dinosaurs
How Animals in Rain Forests Make Themselves Heard
Sociality in Animals
Dinosaurs and Parental Care
Habitat Selection
Temperature Regulation in Marine Organisms
Cell Theory
Poikilotherms
Forest Succession
The Role of Diapause
The Identification of the Genetic Material
How Plants and Animals Arrived in the Hawaiian Islands
Constraints on Natural Selection
