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  3. The temperature of the sun is over 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 16 million degrees

The temperature of the sun is over 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 16 million degrees

admin2012-08-21  47
问题     The temperature of the sun is over 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 16 million degrees at the center. The sun is so much hotter than the Earth that matter can exist only as a gas, except at the core. In the core of the sun, the pressures are so great against the gases that, despite the high temperature, there may be a small solid core. However, no one really knows, since the center of the Sun can never be directly observed.
    Solar astronomers do know that the Sun is divided into five layers or zones. Starting at the outside and going down into the Sun, the zones are the corona, chromosphere, photosphere, convection and the sun has no solid surface, so it is hard to tell where the atmosphere ends and the main body of the Sun begins.
    The sun’s outermost layer begins about 10,000 miles above the visible surface and goes outward for millions of miles. This is the only part of the sun that can be seen during an e-clipse such as the one in February 1979. At any other time, the corona can be seen only when special instruments are used on cameras and other time, the corona can be seen only when special instruments are used on cameras and telescopes to shot out glare of the sun’s rays.
    The corona is a brilliant, pearly white, filmy light, about as bright as the full Moon. Its beautiful rays are a sensational sight during an eclipse. The corona’s rays flash out in a bril-liant fan that has wispy(纤细的) spike like rays near the sun’s north and south poles. The corona is thickest at the sun’s equator.
    The corona rays are made up of gases streaming outward at tremendous speeds and reaching a temperature of more than 2 million degrees Fahrenheit. The rays of gas thin out as they reach the space around the planets. By the time the sun’s corona rays reach the Earth, they are weak and invisible.
The second paragraph is mainly concerned with______.
选项 A、how the sun evolved
B、the structure of the sun
C、why scientists study the sun
D、the distance of the sun from the planets
答案B
解析 这是主旨题，尽管是在提问段落大意。本段的主题句即可说明，本段阐述太阳的构造，而与太阳的进化、科学家研究太阳的成因及太阳距其行星的距离无关，可以说其他选项的信息与本题无多大关系。
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