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  3. The binary planet hypothesis—that Earth and the Moon formed simultaneously by the accretion of smaller objects—does not explain

The binary planet hypothesis—that Earth and the Moon formed simultaneously by the accretion of smaller objects—does not explain

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问题 The binary planet hypothesis—that Earth and the Moon formed simultaneously by the accretion of smaller objects—does not explain why the Moons iron core is so small relative to the Moons total volume, compared with Earth’s core relative to Earths total volume. According to the giant-impact hypothesis, the Moon was created during a collision between Earth and a large object about the size of Mars. Computer simulations of this impact show that both of the objects would melt in the impact and the dense core of the impactor would fall as molten rock into the liquefied iron core of Earth. The ejected matter—mantle rock that had surrounded the cores of both objects—would be almost devoid of iron. This matter would become the Moon.
Which of the following best describes the organization of the passage?
选项 A、The development of one theory into another is outlined.
B、Two explanations are provided, both of which are revealed as inadequate.
C、A theory is presented, and then evidence that undermines that theory is discussed.
D、Similarities and differences between two theories are described.
E、A flawed hypothesis is introduced, and then an alternative hypothesis is presented.
答案E
解析 The passage begins by presenting the binary planet hypothesis about the formation of Earth and the Moon and claiming that the hypothesis fails to explain the disparity in the sizes of Earths iron core and the Moon’s iron core relative to their volumes. The passage then introduces an alternative—the giant-impact hypothesis—and argues that this alternative explains the disparity better. Thus, Choice E is correct. The second theory is not presented as having been developed out of the first, so Choice A is incorrect; only the first theory is revealed as inadequate, so Choice B is incorrect; and the two theories are not compared extensively, so Choice D is incorrect. Although "a theory[the binary planet hypothesis]is presented, and then evidence that undermines that theory[the disparity related to iron cores]is discussed," that description fails to capture the organization of the passage as a whole, so Choice C is incorrect.
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