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Theorists are divided concerning the origin of the Moon. Some hypothesize that the Moon was formed in the same way as were the planets in the inner solar system (Mercury, Venus, Mars, and Earth)—from planet-forming materials in the presolar nebula. But, unlike the cores of the inner planets, the Moon‘s core contains little or no iron, while the typical planet-forming materials were quite rich in iron. Other theorists propose that the Moon was ripped out of the Earth‘s rocky mantle by the Earth‘s collision with another large celestial body after much of the Earth‘s iron fell to its core. One problem with the collision hypothesis is the question of how a satellite formed in this way could have settled into the nearly circular orbit that the Moon has today. Fortunately, the collision hypothesis is testable. If it is true, the mantle rocks of the Moon and the Earth should be the same geochemically.
The author implies that a nearly circular orbit is <D>
unlikely for a satellite that
(A) circles one of the inner planets
(B) is deficient in iron
(C) is different from its planet geochemically
(D) was formed by a collision between two celestial
bodies
(E) was formed out of the planet-forming materials
in the presolar nebula
When a molten metal or metallic alloy is cooled to a solid, a crystalline structure is formed that depends on the particular alloy composition. In contrast, molten
Line nonmetallic glass-forming materials, when cooled, do not
5 assume a crystalline structure, but instead retain a structure somewhat like that of the liquid--an amorphous structure. At room temperature, the natural long-term tendency for both types of materials is to assume the crystalline structure. The difference between the two is in
10 the kinetics or rate of formation of the crystalline structure, which is controlled by factors such as the nature of the chemical bonding and the ease with which atoms move relative to each other. Thus, in metals, the kinetics favors rapid formation of a crystal line structure, whereas
15 in nonmetallic glasses the rate of formation is so slow that almost any cooling rate is sufficient to result in an amorphous structure.
It can be inferred from the passage that, theoretically, molten nonmetallic glasses assume a crystalline structure rather than an amorphous structure only if they are cooled<C>
(A) very evenly, regardless of the rate
(B) rapidly, followed by gentle heating
(C) extremely slowly
(D) to room temperature
(E) to extremely low temperatures
第一篇的那个问题的选项不知道从何而知；第二篇文章的问的是crystalline structure 但答案说的extremely slowly 是对anmorphous structure 而言的，不是吗？谢谢解答。
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发表于 2013-7-7 08:44:32
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