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The dark regions in the starry night sky are not
pockets in the universe that are devoid of stars as
had long been thought. Rather, they are dark because
of interstellar dust that hides the stars behind it.
Although its visual effect is so pronounced, dust is
only a minor constituent of the material, extremely
low in density, that lies between the stars. The average
density of interstellar material in the vicinity of our Sun is
1,000 to 10,000 times less than the best terrestrial
laboratory vacuum. It is only because of the enormous
interstellar distances that so little material per unit of
volume becomes so significant. Optical astronomy
is most directly affected, for although interstellar gas
is perfectly transparent, the dust is not.
According to the passage, which of the following is a direct perceptual consequence of interstellar dust EXCEPT?
答案:B,C

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Reading Comprehension

不太明白这题为什么选C

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