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GRE阅读模拟练习题(230)

2017-05-18 09:35:00来源：网络

　　为了帮助大家练习GRE阅读题考点，新东方在线GRE频道为大家带来GRE阅读模拟练习题一文，希望对大家GRE备考有所帮助。更多精彩尽请关注新东方在线GRE频道!

　　Massive projectiles striking much larger bodies create various kinds of craters, including “multi-ring basins”—the largest geologic features observed on planets and moons. In such collisions, the impactor is completely destroyed and its material is incorporated into the larger body. Collisions between bodies of comparable size, on the other hand, have very different consequences: one or both bodies might be entirely smashed, with mass from one or both the bodies redistributed among new objects formed from the fragments. Such a titanic collision between Earth and a Mars-size impactor may have given rise to Earth’s Moon.

　　The Earth-moon system has always been perplexing. Earth is the only one of the inner planets with a large satellite, the orbit of which is neither in the equatorial plane of Earth nor in the plane in which the other planets lie. The Moon’s mean density is much lower than that of Earth but is about the same as that of Earth’s mantle. This similarity in density has long prompted speculation that the Moon split away from a rapidly rotating Earth, but this idea founders on two observations. In order to spin off the Moon, Earth would have had to rotate so fast that a day would have lasted less than three hours. Science offers no plausible explanation of how it could have slowed to its current rotational rate from that speed. Moreover, the Moon’scomposition, though similar to that of Earth’s mantle, is not a precise match. Theorizing a titanic collision eliminates postulating a too-rapidly spinning Earth and accounts for the Moon’s peculiar composition. In a titanic collision model, the bulk of the Moon would have formed from a combination of material from the impactor and Earth’s mantle. Most of the earthlycomponent would have been in the form of melted or vaporized matter. The difficulty in recondensing this vapor in Earth’s orbit, and its subsequent loss to the vacuum of outer space, might account for the observed absence in lunar rocks of certain readily vaporized compounds and elements.

　　Unusual features of some other planets might also be explained by such impacts. Mercury is known to have a high density in comparison with other rocky planets. A titanic impact could have stripped away a portion of its rocky mantle, leaving behind a metallic core whose density is out of proportion with the original ratio of rock to metal. A massive, glancing blow to Venusmight have given it its anomalously slow spin and reversed direction of rotation. Such conjectures are tempting, but, since no early planet was immune to titanic impacts, they could be used indiscriminately to explain away in a cavalier fashion every unusual planetary characteristic. Still, we may now be beginning to discern the true role of titanic impacts in planetary history.

　　1. According to the passage, which of the following is true of the collisions mentioned in the highlighted sentence?

　　A：They occur less frequently than do titanic collisions.

　　B：They occur between bodies of comparable size.

　　C：They occur primarily between planet-sized bodies.

　　D：They result in the complete destruction of the impacting body.

　　E：They result in mass being redistributed among newly formed objects.

　　答案：D

　　2. The author of the passage asserts which of the following about titanic collision models?

　　A：Such models are conclusive with respect to certain anomalies within the solar system, but leave numerous other anomalies unexplained.

　　B：Such models are more likely than are earlier models to account for the formation of multiring basins.

　　C：Such models may be particularly useful in explaining what happens when the impacting bodies involved are of highly dissimilar mean densities.

　　D：Such models have been tested to such a degree that they are quickly reaching the point where they can be considered definitive.

　　E：Such models are so tempting that they run the risk of being used indiscriminately to explain unusual planetary features.

　　答案：E

　　3. The passage suggests that which of the following is true of the cited “compounds and elements”?

　　A：They were created by reactions that took place during a titanic collision.

　　B：They were supplied by an impactor that collided with Earth.

　　C：They were once present on the Moon but were subsequently vaporized.

　　D：They are rarely found on planet-size bodies in our solar system.

　　E：They are present on Earth but not on the Moon.

　　答案：E

　　4. In the second paragraph, the author is primarily concerned with

　　A：arguing in favor of a particular theory about the formation of the Earth-Moon system.

　　B：summarizing conventional theories about the formation of the Earth-Moon system.

　　C：anticipating and responding to criticisms of particular theory about the formation of the Earth-Moon system.

　　D：explaining why the Earth-Moon system is considered scientifically perplexing.

　　E：questioning an assumption underlying one theory about the formation of the Earth-Moon system.

　　答案：A

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