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  3. The space between the stars is filled with matter that interstellar conditions should prevent from coalescing into solid particl

The space between the stars is filled with matter that interstellar conditions should prevent from coalescing into solid particl

admin2020-03-28  90
问题     The space between the stars is filled with matter that interstellar conditions should prevent from coalescing into solid particle. Yet surprisingly tiny frozen particles, referred to as interstellar grains, do develop in these spaces. These grains are formed out of chemical elements that are synthesized during thermonuclear fusion in stars and supernova explosions.
    The study of interstellar grains has been hampered by the inaccessibility of naturally occurring specimens for use in laboratory experiments. To date, the only source of information about interstellar grains is the stellar electromagnetic radiation that reaches the Earth after passing through regions of space containing interstellar grains. By observing the wavelengths scattered and absorbed by the grains scientists have determined that a grain’s internal structure consists of a core composed of silicates (rocklike material) and a mantle composed entirely of organic compounds. It is hypothesized that each grain begins as a silicate “seedling” ejected from a mature star. Continuous physical and chemical evolution then occurs in the mantle formed around the seedling.
The author uses the term “seedling” most probably in order to
选项 A、suggest that interstellar grains are much smaller than researchers previously assumed
B、suggest the fragility of the process of interstellar grain formation
C、characterize one kind of interstellar grain
D、suggest that most interstellar grains begin as small particles and grow into larger bodies
E、describe the organic nature of interstellar matter
答案D
解析 本题属于功能题，定位部分的3s版本便是在介绍星际颗粒的形成过程，因此选项D正确。
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本试题收录于： GRE VERBAL题库GRE分类
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