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  3. The finding that there were rock-melting temperatures on asteroids for sustained periods is puzzling: asteroids’ heat source is

The finding that there were rock-melting temperatures on asteroids for sustained periods is puzzling: asteroids’ heat source is

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问题     The finding that there were rock-melting temperatures on asteroids for sustained periods is puzzling: asteroids’ heat source is unknown, and unlike planet-sized bodies, such small bodies quickly dissipate heat. Rubin suggests that asteroids’ heat could have derived from collisions between asteroids. Skeptics have argued that a single impact would raise an asteroid’s overall temperature very little and that asteroids would cool too quickly between impacts to accumulate much heat. However, these objections assumed that asteroids are dense, solid bodies. A recent discovery that asteroids are highly porous makes Rubin’s hypothesis more plausible. When solid bodies collide, much debris is ejected, dissipating energy. Impacts on porous bodies generate less debris, so more energy goes into producing heat. Heat could be retained as debris fall back into impact craters, creating an insulating blanket.
The passage suggests that one factor that has made it difficult to account for the temperatures once reached by asteroids is
选项 A、a miscalculation of the frequency of asteroid collisions
B、a misconception about asteroids’ density
C、a mistaken assumption about what the heat source of the asteroids was
D、an underestimation of the rate at which small bodies lose heat
E、an erroneous view of how asteroids were formed
答案B
解析 根据第一句可知，关于小行星温度的解释的困难主要在于热源和散热。根据怀疑者的观点可推导出，正是因为他们错误地假设了小行星是高密度的，才导致人们无法理解小行星的热源以及散热速度。之后人们发现小行星是多孔结构的，这时有关小行星热量的困惑就得到了解释，因此答案是选项B。
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