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  3. Reading According to the controversial sunspot theory, great storms on the surface of the Sun hurl streams of solar particles in

Reading According to the controversial sunspot theory, great storms on the surface of the Sun hurl streams of solar particles in

admin2018-06-21  78
问题 Reading
According to the controversial sunspot theory, great storms on the surface of the Sun hurl streams of solar particles into space and eventually into the atmosphere of our planet, causing shifts in the weather on the Earth and interference with radio and television communications.
A typical sunspot consists of a dark central umbra, a word derived from the Latin word for shadow, which is surrounded by a lighter penumbra of light and dark threads extending out from the center like the spokes of a wheel. Actually, the sunspots are cooler than the rest of the photosphere, which may account for their apparently darker color. Typically, the temperature in a sunspot umbra is about 4000 K, whereas the temperature in a penumbra registers 5500 K, and the granules outside the spot are 6000 K.
Sunspots range in size from tiny grains to complex structures with areas stretching for billions of square miles. About 5 percent of all sunspots are large enough so that they can be seen from Earth without instruments; consequently, observations of sunspots have been recorded for thousands of years. They have been observed in arrangements of one to more than one hundred spots, but they tend to occur in pairs. There is also a marked tendency for the two spots of a pair to have opposite magnetic polarities. Furthermore, the strength of the magnetic field associated with any given sunspot is closely related to the spot’s size.
Sunspots have also been observed to occur in cycles, over a period of eleven years. At the beginning of a cycle, the storms occur between 20 and 40 degrees north and south of the equator on the Sun. As the cycle continues, some of the storms move closer to the equator. As the cycle diminishes, the number of sunspots decreases to a minimum, and they cluster between 5 and 15 degrees north and south latitude.
Although there is no theory that completely explains the nature and function of sunspots, several models show scientists’ attempts to relate the phenomenon to magnetic field lines along the lines of longitude from the north and south poles of the Sun.
What is the author’s main purpose in the passage?
选项 A、To describe the nature of sunspots
B、To propose a model for cycles in the solar year
C、To compare the umbra and the penumbra in sunspots
D、To argue for the existence of magnetic fields in sunspots
答案A
解析
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