If it is true that the streets and the sidewalks are wet whenever it is raining, which of the following must also be true?
I. If the streets and sidewalks are wet, it is raining.
II. If the streets are wet but the sidewalks are not wet, it is not raining.
III. If it is not raining, the streets and sidewalks are not wet.
(A) I only
(B) II only
(C) III only
(D) I and II only
(E) II and III only
The correct answer is (B)
can anyone tell me why? 看了老半天还是搞不清楚...
答案是B。
意思就是问:无论何时下雨,街道和人行道就会湿。
1:如果街道和人行道湿了,一定是下雨----不一定,也许是洒水车搞的;
2:如果街道湿了,但是人行道没湿,一定没有下雨---正确,因为如果下雨,两个都会湿;
3:如果没有下雨,街道和人行道不会湿---和1一样,也许是洒水车来了。
嗯...我想通了
原本我是用A=B+C的角度看这题
但应该要用cause and effect的观点才正确
雨"cause" both 人行道&街道wet
但是 人行道&街道wet不一定是"cause only by"雨
这个是lsat的题目吧?
我个人认为A=如果下雨,B=街道和人行道肯定湿。A=》B,那么只有非B=》非A才是答案准确的。。
所以只有答案2
下雨=A
街湿=B1
人行道湿=B2
原命题:A -〉B1,B2
逆否:B1,否B2 -〉否A
否B1,B2 -〉否A
否B1,否B2 -〉否A
原命题正确,只有逆否命题正确,其他全错
所以根本不用想:选B
LS正解,原命题: it is raining=streets are wet+sidewalks are wet 逆否一下,LZ再试试
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