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题库 / Prep2012-SC-69
Laboratory rats and mice live up to 40 percent longer than usual when fed a diet of at least 30 percent fewer calories than that which they would normally eat, but that otherwise contains all necessary vitamins and nutrients.
of at least 30 percent fewer calories than that which they would normally eat, but that otherwise
with at least 30 percent fewer calories than what they would normally eat though otherwise it
that has at least 30 percent fewer of the calories that they would normally eat, but otherwise it
that has at least 30 percent fewer calories than they would normally eat but that otherwise
that has at least 30 percent fewer calories than that which they would normally eat, though that otherwise
题目分析：
首先，具有fewer calories than关系的两者应该是a diet和a diet that they would normally eat，所以than后需要写出比较的对象（时态或情态等任何的不同均不能省略），即they would normally eat，可以排除(A)(B)(E)。其次，在本题中，具有转折关系的两者是“卡路里比以前吃的饭少了30%（at least 30 percent fewer calories than they would normally）”和“所有的营养以及维他命是一样的（contains all necessary vitamins and nutrients）”，即，这个diet中，虽然某些“坏东西”少了，但是“好东西”没有什么变化，因此has at least 30 percent应该和contains all necessary vitamins and nutrients平行，可以排除(C)，答案为(D)。
选项分析：
略
选项A：首先，a diet of 表示 “一种......的饮食习惯”，而划线部分是想描述diet 的特点；其次，but 之后是一个定语从句，而 but 之前找不到与之并列的对象；至于than 之后的that，可以指代 diet，同类不同物，所以 that which 没有错误。
选项B：what they would normally eat扩大了语义范围，包含了老鼠所有吃的内容，从而改变了比较双方造成不可比；同时，though 表示让步，语义变成 “虽然它包含了必需的维生素和营养” ，“但是热量还是少了百分之30”，可以理解为 “维生素和营养” 其实并不重要。而 but 表示转折，“虽然热量比平时diet的热量少30%，但是它含有所有必需的维生素和营养”，逻辑更准确。
选项C：but之后是一个完整句子结构。导致 contains 与 live up 并列转折；逻辑上应该是contains 与 has 并列，表示转折；看不出来也没关系，马上看到选项D 就知道选项C 的错误了。
选项D：正确
选项E：与选项B 同理，though 表示让步关系，表达不准确。
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