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  3. When we accept the evidence of our unaided eyes and describe the Sun as a yellow star, we have summed up the most important sing

When we accept the evidence of our unaided eyes and describe the Sun as a yellow star, we have summed up the most important sing

admin2014-08-25  61
问题     When we accept the evidence of our unaided eyes and describe the Sun as a yellow star, we have summed up the most important single fact about it—at this moment in time. It appears probable, however, that sunlight will be the color we know for only a negligibly (微不足道的) small part of the Sun’s history.
    Stars, like individuals, age and change. As we look out into space, we see around us stars at all stages of evolution. There are faint blooded dwarfs so cool that their surface temperature is a mere 4, 000 degrees Fahrenheit; there are scaring ghosts blazing at 100, 000 degrees Fahrenheit and almost too hot to be seen, for the great part of their radiation is in the invisible ultraviolet range. Obviously, the "daylight" produced by any star depends on its temperature; today (and for ages to come) our Sun is at about 10, 000 degrees Fahrenheit, and this means that most of the Sun’s light is concentrated in the yellow band of the spectrum, falling slowly in intensity toward both the longer and shorter light waves.
    That yellow "hump" will shift as the Sun evolves. and the light of the day will change accordingly. (80) It is natural to assume that as the Sun grows older, and uses up its hydrogen fuel—which it is now doing at the spanking rate of half a billion tons a second—it will become steadily colder and redder.
What is the passage mainly about?
选项 A、Faint dwarf stars.
B、The evolution cycle of the Sun.
C、The Sun’s fuel problem.
D、The dangers of invisible radiation.
答案B
解析 本题为主旨题。本文主要是谈太阳的演化周期，所以为B。对A项为微红的矮星、C项为太阳的燃料问题，都只是一带而过．不可作为本文的中心议题。本文没有谈及D项的不可见辐射的危险。
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