***归纳：陈向东归纳一章的一类题***

以下题目都是类似的：

67。All actors are exuberant people and all exuberant people are extroverts, but nevertheless it is true that some shy people are actors.

If the statements above are true, each of the following must also be true EXCEPT:

A. Some shy people are extroverts.

B. Some shy extroverts are not actors.

C. Some exuberant people who are actors are shy.

D. All people who are not extroverts are not actors.

E. Some extroverts are shy.

72。No senator spoke at the convention unless he or she was a Democrat. No Democrat both spoke at the convention and was a senator.

Which one of the following conclusions can be correctly drawn from the statements above?

A. No one but senators spoke at the convention.

B. No Democrat spoke at the convention.

C. Only Democrats spoke at the convention.

D. No senator spoke at the convention.

E. Some Democrat senators apoke at the convention.

73. Some of the world's most beautiful cats are Persian cats. However, it must be acknowledged that all Persian cats are pompous, and pmpous cats are invariably irritating.

If the statements above are true, each of the following must also be true on the basis of them EXCEPT:

A. Some of the world's most beautiful cats are irritating.

B. Some irritating cats are among the world's most beautiful cats.

C. Any cat that is not irritating is not a Persian cat.

D. Some pompous cats are among the world's most beautiful cats.

E. Some Irritating and beautiful cats are not Persian cats.

74. Most parents who are generous are good parents, but some self-centered parents are also good parents. Yet all good parents share one characteristic: they are good listeners.

If all of the statements in the passage are true, which one of the following must also be true?

A. All parents who are good listeners are good parents.

B. Some parents who are good listeners are not good parents.

C. Most parents who are good listeners are generous.

D. Some parents who are good listeners are self-centered.

E. Fewer self-centered parents thatn generous parents are good listeners.

不完全归纳：

上面题目都能牵涉的问题：

1. 首先列出充分必要条件的逻辑链条，公共元素直推归纳（by 费费）：

If /When A, then B.                A→B

Only if A, then B.                   B→A

Must by A, in order to B.        B→A

If only A, then B.                  A→B

Not A, unless B.                    A→B

A, unless B.                          否B→A, 否A→B

A require B.                         A→B

A is necessary to B.              B→A

A depend/draw/base on B.     A→B

2. 知识点：原命题=逆否，不等于否/逆，但可以等于“部分”逆命题，理论依据是必要条件不能做为结论的充分条件、但却可以是结论的“部分”条件

3. 对程度副词的取非：（by Lawyer) 

   all----not all/some---none/always----not always/sometimes----never/everywhere---not everywhere/somewhere---nowhere/only one, exactly one---none, more than one/at least one, some---none

4. A -> C,D 则逆否有3种情况:     否C,D -> 否A，  C,否D -> 否A，否C,否D -> 否A     

5. 经验：A,B -> C,D 如果出现把A,B中的一个元素和C,D中的一个元素合并推出剩余一些元素，则是错误答案的标志

6.善用Venn diagram.