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在题干中看到虚拟语气，大多需要用到取非思想，与之相对应的一种题型是GRE阅读题中常见的一种，叫做改进型取非题。看例子之前，先简单解释下什么是改进型取非题。很简单，如果题干问如果一个对象怎样会更好则是改进型取非题，来看具体的例子： 例：It can be inferred from the passage that the first theories of grazer control mentioned in line 3 would have been more convincing if researchers had been able to,这是一个典型的改进型取非题题干，问的是第三行第一个理论怎样会更好。 逻辑思路：既然是改进，原文肯定说到了它的不好之处或者有unless的句子，我们把造成不好的原因取非，就是所要的答案了。 按照此思路定位原文三行，看到后面有这样一句话A low number of algal cells in the presence of a high number of grazers suggested, but did not prove, that the grazers had removed most of the algae.注意看插入语部分的but did not prove，这个就是缺点，取非就是prove再看五个选项： observe high phytoplankton numbers under natural lake conditions discover negative correlations between algae and zooplankton numbers from their field research understand the central importance of environmental factors in controlling the growth rates of phytoplankton | 
