求救，老师讲义上的题目

上课的时候老师讲解过了，可是笨笨的我还是不明白，绕来绕去，头都晕了，特请大家帮忙，先谢！

答案是d可是我不知道如何推导出，以及如何排除b

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

a. no one but senators spoke at the convention.

b. no Democrat. spoke at the convention.

c.only Democrat spoke at the convention,

d. no senator spoke at the convention.

e. some Democrat senators spoke at the convention.

这是在考逆否命题

第一句化简如下：a senator was not a Democrat-->this senator not spoke

第二句作如下解释：一个D不可能既是一个senator又发了言

第一句的逆否命题：a senator spoke-->this senator was a Democrat

结合第二句，这个D既然是senator了，那么就不可能发言了；事实只能是没有senator发言。

关于B，可能有的D发了言但不是senator,这也是符合原文推理的

Any senator spoke at the convention  推出     he or she was a Democrat.(第一句)

he or she was a Democrat    推出    either not spoke or not a senator(第二句)

Any senator spoke at the convention    推出    either not spoke or not a senator

So anwer d is right. Got it ?

如果还不明白，就将最后一个推力取逆否命题

即：spoke and a senator 推出 no senator spoke at the convention

明白了，谢谢二位，做逻辑题真的挺困难的，根据题目我都能得出两个推理，但是就是想不通如何到结论去了，脑子好像进水了一样

再次感谢！！

建议看看lawyer_1的考试时如何做逻辑，非常棒的！