大全3-8
8. By analyzing the garbage of a large number of average-sized households, a group of modern urban anthropologists has found that a household discards less food the more standardized—made up of canned and prepackaged foods—its diet is. The more standardized a household’s diet is, however, the greater the quantities of fresh produce the household throws away.
Which of the following can be properly inferred from the passage?
(A) An increasing number of households rely on a highly standardized diet.
(B) The less standardized a household’s diet is, the more nonfood waste the household discards.
(C) The less standardized a household’s diet is, the smaller is the proportion of fresh produce in the household’s food waste.
(D) The less standardized a household’s diet is, the more canned and prepackaged foods the household discards as waste.（C）
(E) The more fresh produce a household buys, the more fresh produce it throws away.
不明白为什么是C呀。C明明是已知的否命题怎么能对呢？
大全-3-19
19. Black Americans are, on the whole, about twice as likely as White Americans to develop high blood pressure. This likelihood also holds for westernized Black Africans when compared to White Africans.Researchers have hypothesized that this predisposition in westernized Blacks may reflect an interaction between western high-salt diets and genes that adapted to an environmental scarcity of salt.
Which of the following statements about present-day, westernized Black Africans, if true, would most tend to confirm the researchers’ hypothesis?
(A) The blood pressures of those descended from peoples situated throughout their history in Senegal and Gambia, where salt was always available, are low.
(B) The unusually high salt consumption in certain areas of Africa represents a serious health problem.
(C) Because of their blood pressure levels, most White Africans have markedly decreased their salt consumption.
(D) Blood pressures are low among the Yoruba, who, throughout their history, have been situated far inland from sources of sea salt and far south of Saharan salt mines.
(E) No significant differences in salt metabolism have been found between those people who have had salt available throughout their history and those who have not.
只有逆否命题和原命题等价吧 (A->B <=> -B->-A)
非常的不理解为什么A -> B here is: -A -> -B
谢谢NN帮忙解释这2道小题目！
急坏我了，似乎我概念上转不过来呀，想了好几天了都！
顶！
逻辑术语，我一点也不懂
3-8
两个判断:1. less food---more standard; 2. more standard----more garbage of fresh produce
1.2.---->more standard, high propotion of fresh produce in the food waste
反过来，less standard,就是c吧。
比较菜，第2我也不懂，共勉
感觉你认真的挺可爱的，刚才一直在想这问题，希望自己能帮助你。
一开始就google什么等价命题，什么逆反关系， 除了太阳穴疼，血压上升，想发狂，没其他收获。
后来，我感觉这个地方可能有个误区：你是对的，但是
你说的A=>B 等价 -B => -A是不是跟讨论贴他们说的A=> B -A=>-B意思不一样？？
我感觉楼上两到题目，不涉及所说等价命题，只是涉及正相关或者负相关关系。
例如 3-8
饮食越标准化 扔掉的新鲜食物比例越多 说明了，饮食的标准化程度跟新鲜食物垃圾比例成正比。所以呢，反过来，越不标准，新鲜垃圾比例就低
例如3-19 感觉是阅读理解题，半天才看懂，ets真有点可爱过头
原文： 高血压跟基因适应盐的程度成反比
A: 显示了这样一种反比， 适应盐能力强， 血压低， 所以是支持原文的
供讨论，希望对你有启发
我有个建议
晚上千万别复习逻辑。
我也刚开始复习逻辑不到一星期，要是晚上复习了，睡眠就暴差，后遗症就多了
谢谢jxjiao给的建议，但是第一题目还是觉的不对，我举一道FF上的逻辑
27. These days, drug companies and health professionals alike are focusing their attention on cholesterol in the blood. The more cholesterol we have in our blood, the higher the risk that we shall die of a heart attack. The issue is pertinent since heart disease kills more North Americans every year than any other single cause. At least three factors---smoking, drinking, and exercise—can each influence levels of the cholesterol in the blood.
Which one of the following can be properly concluded from the passage?
A. If a person has low blood cholesterol, then that person’s risk of fatal heart disease is low.
B. Smoking in moderation can entail as great a risk of fatal heart disease as does heavy smoking.
C. A high-cholesterol diet is the principal cause of death in
D. The only way that smoking increases one’s risk of fatal heart disease is by influencing the levels of cholesterol in the blood.
E. The risk of fatal heart disease can be altered by certain changes in lifestyle.
答案是E。解释：
A. 原文中说，胆固醇越高，生心脏病的可能性越大。A选项的内容是否命题，不一定成立。
第一题和这道不是一样的道理？为什么第一题的否命题在这成立呢？
关于第二题目，还是想CONFIRM一下是否在加强题目中-A -> -B是用来加强A -> B的，作题中还没有遇到类似的。
还请大家帮忙拉！！
呵呵，偶找不到窍门，只能帮你顶啦。
没形成规律，个人只有具体题目具体分析，扔垃圾的那道题目涉及的关系比较简单，注重比例关系。 上面这题目，我看了题，就马上会联想还有其他风险的，找答案的关键词：是smoking,drinking,and exercise 和 risk
呵呵，知道了你的答案也告诉我哦，要是有万能的规律确实很好，会加快速度
还是要接着顶呀！
NN们快出来帮帮忙吧！
还没有人出来帮帮忙呀？
再顶！
顶呀顶，NN们出来帮忙呀！
还是没有人出来帮忙呀！
各位斑竹以及LAWYER怎么不出来帮忙答答疑呀？
谢谢喽！
再顶！
还是顶，怎么就没有人出来帮帮忙呢？
看来你比较喜欢纯数学和逻辑。我们就用理论来陈述吧：
FF题的A选项不对，因为是开放集合的否命题。[开放集合中，逆否命题等价于原命题]低胆固醇+正常+高胆固醇=全集；心脏病方面也是一样。
8中，集合性质不同：A，B类互补；X，Y也互补。且A对应X，B对应Y；对应关系唯一。因此，A对应X的否命题，其实并不是等价于该原命题，应理解为：非A对应非X，即（引入集合）：B对应Y。
最后，GMAT的逻辑题，如果不是从选优角度考虑，严格来说，没有正确的。重要的是找到ETS的出题感觉，而不是从中学习逻辑。不要走太远了。GMAT不是全部。
顶了半天终于有人帮忙了，谢谢楼上！
开放集合的定义我不太懂！
你的意思是不是说8题中The more standardized a household’s diet is, however, the greater the quantities of fresh produce the household throws away. 它们的关系在原题中陈述的就是正比的关系（文中没有提到别的因素影响它们之间的关系）。而FF那道题目中有说要考虑别的因素？
3-8是指anthropologist发现的correlation
FF中的由于其他原因也可能造成fatal heart disease,所以low blood pressure 不一定就low risk of fatal heart disease
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