职称英语考试理工类完形填空基础练习及答案(5)

　　Structure of the Sun

　　1 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.

　　2 Solar astronomers do know that the Sun is divided into five layers of zones. Starting at the outside and going down into the sun, the zones are the corona, chromosphere, photosphere, convection zone, and finally the core. The first three zones are regarded as the Suns 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.

　　3 The Suns outermost layer begins about l0000 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 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 Suns rays.

　　4 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 coronas rays flash out in a brilliant fan that has wispy spider-like rays near the Suns north and south poles. The corona is thickest at the Suns equator.

　　5 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 planet. By the time the Suns corona rays reach the Earth, they are weak and invisible.

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　　A.Basic description of the core

　　B. Characteristics of the corona

　　C. The composition of the corona rays

　　D. Five layers of zones of the sun

　　E. Characteristics of the corona rays

　　F. The eclipse in February 1979

　　正确答案:DBEC