【2017年整理】申友GMAT培训阅读解析—讲义·科普类.doc

申友GMAT培训阅读解析—讲义·科普类·Passage 4 GMAT阅读即GMAT阅读理解（Reading Comprehension），也称GMAT阅读RC。GMAT阅读RC属于GMAT考试写作、数学和语文中的语文部分。考试中提供阅读文章三或四篇，共设25个问题，每个问题有四个可供选择的答案。文章内容涉及到人文科学、社会学、物理学和生物学等领域“keystone” species, here defined as one whose effects are much larger than would be predicted from its abundance（对“keystone” species的解释，跳读时先不读具体内容）, can also play a vital role. // But （表转折的词要注意逻辑方向的变化）because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic（关于identifying a keystone species的问题，用RO的方式是不正确的。要注意后文是否提出的其他解决方法）. // It might seem that certain traits would clearly define a species as a keystone species（开始提出一种观点：根据某些特征可以识别）; for example（举例说明。例子内容跳读时不读，但要知道它是服务于其前那个观点的）, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But(注意逻辑方向的变化) such（注意指代的对象，即P-M predation）predation on a dominant or potentially dominant species occurs in systems that do as well as in system that do not have species that play keystone roles. Moreover（表递进的连接词，逻辑方向不变）, whereas P.ochraceus occupies an unambiguous keystone role on wave-exposed rocky headland, in more wave-sheltered habitats the impact of P.ochraceus predation is weak or nonexistent（注意此处的比较，比较对象是the impact of P.ochraceus predation，对比因素是wave-exposed and wave-sheltered habitats）, and(并列连接词，连接的是削弱P.ochraceus predation的另一种情况) at certain sites an sand burial is responsible for eliminating mussels. // Keystone status appears to depend on context（提出第二个观点，也是对identifying a keystone species这个问题的解决方案，即depend on context）, whether of particular geography（决定keystone status的第一个因素） or of such factors as community diversity（决定keystone status的第二个因素） (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction（决定keystone status的第三个因素） (since newly arrived species in