请教：feifei逻辑的58题（虽然看了旧帖仍然不太明白）

winterain

58. Some people say that the scarcity of food is a function of the finite limits of the earth’s resources, coupled with a relentless rate of population growth. This analysis fails to recognize, however, that much of the world’s agricultural resources are used to feed livestock instead of people. In the United States, for example, almost one-half of the agricultural acreage is devoted to crops fed to livestock. A steer reduces twenty-one pounds of inexpensive grain to one pound of expensive meat. Thus, the scarcity of food is not merely a function of limited resources and population growth.
Which one of the following is an assumption that would allow the conclusion in the argument to be properly drawn?  
A. People prefer eating meat to eating grain.
B. Meat is twenty-one times more expensive than grain.
C. The limits of the earth’s agricultural resources are not finite.
D. More than one-half of the agricultural acreage in the United States is devoted to drops fed to humans.
E. Growing crops for human consumption on the acreage currently devoted to crops for livestock will yield more food for more people.
OA is E.
请大家帮忙给我分析一下整个reasoning的过程，谢谢。
不用和我说，E项取非否定结论所以选它，这个我知道。
恳请各位不吝赐教。

sdcar2010

The way to find a necessary assumption is to negate the assumption and if negating an answer choice causes the argument to fall apart, then that choice is the correct answer.

However, in this question, the question stem asks for a sufficient or justifying assumption.  Therefore, we need to find something that must be true in order to reach the conclusion of the argument. If an answer choice does not need to be true (for example, it could be true or it could be false), then that choice is not a sufficient assumption.

Let's take a look at the argument.

Facts: 1) Much of the world’s agricultural resources are used to feed livestock instead of people.
          2)Twenty-one pounds of inexpensive grain is converted to one pound of expensive meat.

Conclusion: The scarcity of food is not merely a function of limited resources and population growth.

Hmmm.  Then there must be something else that can cause the food shortage. Since we know the facts 1) and 2), it is reasonable to say that the shortage might also be a funtion of the amount of grain converted into meat.
Answer E) states that growing crops on land devoted to growing crops for livestock will yield more food for more people.  (E) not only identifies a way to solve the food scarcity problem, but also confirms that there is a third factor for the same problem - land devoted to grow crops for livestock.  Thus, E is a justifying assumption.

winterain

The way to find a necessary assumption is to negate the assumption and if negating an answer choice causes the argument to fall apart, then that choice is the correct answer.

However, in this question, the question stem asks for a sufficient or justifying assumption.  Therefore, we need to find something that must be true in order to reach the conclusion of the argument. If an answer choice does not need to be true (for example, it could be true or it could be false), then that choice is not a sufficient assumption.

Let's take a look at the argument.

Facts: 1) Much of the world’s agricultural resources are used to feed livestock instead of people.
          2)Twenty-one pounds of inexpensive grain is converted to one pound of expensive meat.

Conclusion: The scarcity of food is not merely a function of limited resources and population growth.

Hmmm.  Then there must be something else that can cause the food shortage. Since we know the facts 1) and 2), it is reasonable to say that the shortage might also be a funtion of the amount of grain converted into meat.
Answer E) states that growing crops on land devoted to growing crops for livestock will ield more food for more people.  (E) not only identifies a way to solve the food scarcity problem, but also confirms that there is a third factor for the same problem - land devoted to grow crops for livestock.  Thus, E is a justifying assumption.

-- by 会员 sdcar2010 (2010/12/23 11:21:16)

hi, sdcar, thanks for your answer.
看过你的解释我又想了一下，E选项应该是establish the feasibility of the premise of the conclusion. 也就是你说的confirm。
然后自己又缕了一遍思路：
原文中提到scarcity of food还有一个原因是因为feed livestock，E正是establish the feasibility of this premise。原文中提到feed livestock消耗掉了much of the agricultural resources，但这不一定代表会造成食物短缺；而one-half of the agricultral acreage is devoted to crops fed to livestock，也无法推理出一定造成了食物短缺，因为这些livestock还可以为people提供food；steer的举例同样也不能完全证明，因为可能人如果吃meat只能吃one pound而吃grain则要吃21 pounds。
所以也就是说原文给出的三个论据都不能足够支撑它的结论，而E则在比较中明确提出了短缺的意思：那些被用做为crops for livestock consumption生长的土地，（如果）用于供crops for human consumption生长，能够（比前者）生产更多食物提供给更多人。

gamxiaoyuan

这个帖子写得太好了，忍不住要顶一下！！！