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题库 / GMATAdvanced-CR-2
Recent observations suggest that small, earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy other than the sun. Of over two hundred planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun.
Which of the following, if true, would most weaken the above justification of the claim that earthlike worlds form a low percentage of the total number of planets?
There are millions of planets orbiting stars around which astronomers have not attempted to detect planets.
The best current astronomical theories predict that almost all planets around other stars are probably hundreds of times larger than the earth.
A planet orbiting a star similar to the sun would be more likely to be earthlike in size than would a planet orbiting a much smaller star.
The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.
The observations would have detected any small, earthlike worlds orbiting the stars around which larger planets have been detected.
P：观测的两百多个行星（绕着别的恒星转的），几乎全部都有地球的几百倍大 几百倍重，而且他们环绕的恒星比太阳小多了（因）
C：银河系里，除太阳系以外的星系，围绕恒星运行的行星中，体积小的类地行星比例很低（果）
先观测再得出结论，所以是因果推理：攻击结论，or，攻击前提的有效性（样本数据代表性）
• AThere are millions of planets orbiting stars around which astronomers have not attempted to detect planets. （这个选项确实和P有关，但是无法攻击P的样本有效性，因为就算再观测几百万个行星，这几百万个既可能都很大（不类地），也可能类地，所以无法说明“类地行星占比小”是错的）
A的问题：样本有代表性不是说数量足够多就是加强，而是要能推出结论的样本足够多才是加强
A选项还有很多未观测到的行星可能是类地行星也可能不是，所以这个选项并不能加强结论
• BThe best current astronomical theories predict that almost all planets around other stars are probably hundreds of times larger than the earth. （这是支持结论的）
• CA planet orbiting a star similar to the sun would be more likely to be earthlike in size than would a planet orbiting a much smaller star. （无关，原文的结论是类地行星在太阳系以外的星系占比小，而不是与太阳系相似的星系）
• DThe smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect. （攻击前提的样本有效性：说明科学家探测结果不准，也许有很多类地但是没有观测到；如果脑子转不过来，取非：行星相对恒星越小，越好观测，那么这么好观测的情况下都观测不到几颗，说明确实占比小，取非加强，该选项为削弱；另外这里其实也有暗示了行星与恒星的相对大小）
• EThe observations would have detected any small, earthlike worlds orbiting the stars around which larger planets have been detected. （这里说，这个实验应该能观测那些大行星环绕恒星的星系中的小星球，这个选项其实说明科学家是观测了的，还得出了占比小的结论，是对原来结论的加强）
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