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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

admin2012-07-17  43
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 (日冕, 光环层)，chromosphere (色球层)，photosphere (光球层)，convection zone(对流层)，and finally the core. The first three zones are regarded as the Sun’s atmosphere. But since the Sun has no solid surface, 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 eclipse (日 食) 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 telescopes to shut out the 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 brilliant 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 two 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.
What is the main topic of the passage?
选项 A、The great pressures of the Sun.
B、The high temperature of the Sun.
C、The structure of the Sun.
D、How the Sun evolved.
答案C
解析 本题问本文的主题是什么。利用浏览式阅读法通读全文内容和重点词句，我们可以推断出本文的中心思想是介绍太阳的结构。因此，本题的正确答案应是C。
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