有些逻辑题可真是弯弯绕---请教陈向东书中2题

我发现自己做题时，凭第一感觉选，倒还有一定正确率。如果再多想想，越想得多反而越复杂、越糊涂。估计是进了牛角尖，找不到出路了。看来还是不得要领。

现在请教2个题：

1.  Dormitories range from two to six stories in height. If a dormitory room is above the second floor, it has a fire escape. If the statements above are true, which of the following must also be true?

A.  Second-floor dorm rooms do not have fire escapes.

B.  Third-floor dorm rooms do not have fire escapes.

C.  Only dormmitory rooms above the second floor have fire escapes.

D.  4th floor dormitory rooms have fire escapes.

E.  some two-story dormitories do not have fire escapes.

答案是D。 毫无疑问D是对的。但A不也对吗？当然如果分析A为否命题，就不对。可从意思上想不通为什么不对。请指教。谢谢。

2。 Large national budge deficits do not cause large trade deficits. If they did, countries with the largest budget deficits would also have the largest trade deficits. In fact, when deficit figures are adjusted so that different countries are reliably coparable to each other, there is no such correlation. If the statements above are all true, which of the following can properly be inferred on the basis of them?

A.  Countries with large national budget deficits tend to restrict foreign trade.

B.  Reliable comparisons of the deficit figures of one country with those of another are impossible.

C.  Reducing a country's national budget deficit will not necessarily result in a lowering of any trade deficit that country may have.

D.  When countries are ordered from largest to smallest in terms of population, the smallest countries generally have the smallest bedget and trade deficits.

E.  Countries with the largest trade deficits never have similarly large national budget deficits.

answer: C

关于E，是不是可以这样理解：因段落中没有never have similarly large national budget deficits这样的info，它属于无关？我是被陈向东的解释弄糊涂的。他说：E （贸易赤字最大的国家有时--应该是从未---有类似的巨额预算赤字）与该短文没有矛盾。没矛盾不正好吗？怎么成了错项的标准了呢？（他在好几个归纳题里的解释选项错误的原因是“该短文没有矛盾”）

请明白人指教。谢谢谢谢。

提干的意思是：宿舍是从2楼都6楼，如果宿舍超过2楼，那么必须得有fire escape

a选项是两层楼的宿舍没有消防通道，虽然有这种可能性，但是原题并没有完全表示这个意思，两层楼的宿舍可能也有消防通道

其实这是个充分条件的假言推理

形式如下

if p, then q                      if p, then q

p                               ﹁q

q                               ﹁p

肯定前件式

(p→q)∧p→q

否定后件式

(p→q)∧﹁q→﹁p

充分条件的假言推理有以下规则

肯定前件就要肯定后件，否定后件就要否定前件

否定前件不能否定后件，肯定后件不能肯定前件

不要灰心，仔细体会下