哎呀...

linlin315

有关命题关系的一些问题
1、Mass transit authorities in large cities are struggling with deficits. Riders complain about delays and breakdowns, cuts in service, and fares higher than they are accustomed to paying. For all these reasons and because the price of gasoline is still not prohibitive, the number of passengers using public transportaion has fallen, adding to the deficits.
Which of the following statements about the relationship between the number of riders using public transportation and the price of gasoline rises, is best supported by the passage above?
A. As the price of gasoline rises, the number of riders using public transportation rises
B. Even if the price of gasoline rises, the number of riders using public transportation will continue to decline.
C. If the price of gasoline rises to a prohibitive level, the number of riders using public transportation will rise
D. The majority of riders using public transportation do not use gasoline; hence, fluctuations in gasoline prices are unlikely to affect the number of riders using public transportation
E. The price of gasoline is always low enough to make private transportation cheaper than public transportation; hence, fluctuations in gasoline prices are unlikely to affect the number of riders using public transportation.
答案是C
可是C的逆否命题是the mumber will not rise---->the price does not rise to a prohibitive level怎么能和文章中的命题the price is not prohibitive--->the number has fallen一样呢。

小米

文章中的命题the price is not prohibitive--->the number has fallen一样呢。
(反了，实际上THE PRICE NOT PROHIBITIVE是THE NUMBER FALLEN的必要条件，因为文中是说其他原因+PRICE原因导致THE NUMBER FALLEN，所以PRICE原因不是充分条件，因此关系为THE NUMBER FALLEN--》THE PRICE IS NOT PROHIBITIVE。
由于本题是从上往下题，取逆否命题得结论C。

linlin315

可是小米
because a, b得逻辑推理关系不应该是a--->b吗？？？

小米

but LinLin, "For all..........and because ............“是并列结构，就是A+B--》C， 那么A或B应该是C的必要条件，而非充分条件。

linlin315

可是小米，还有个问题就是对于THE NUMBER FALLEN--》THE PRICE IS NOT PROHIBITIVE。取逆否应该是the price is prohibitive--->the number does not fall
not fall并不一定就代表rise啊？？你说对不？他还可能不变呢？可是C中的是rise??怎么回事？

以下是引用小米在2003-7-25 14:03:00的发言：
THE NUMBER FALLEN--》THE PRICE IS NOT PROHIBITIVE。
由于本题是从上往下题，取逆否命题得结论C。

小米

小米投降了，望哪位斑竹解救：）