请教逻辑题，lsat练习中

夏日飘雪

6. 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) N 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 spoke at the convention.

答案是D，为什么不选C?

8. Neuroscientists are making progress in discovering more about the cause of Alzheimer’s disease. Alzheimer’s disease patients suffer from dementia and sever memory loss. Autopsies performed on such patients have revealed the presence of brain lesions caused by abnormal protein deposits. Similar deposits are also found in the brains of elderly patients who do not suffer from Alzheimer’s disease. It follows that everyone who lives long enough will eventually develop Alzheimer’s disease.

Which one of the following statements, if true, most seriously undermines the conclusion that everyone who lives long enough will eventually develop Alzheimer’s disease?

(A) The lesions found in the brains of non-Alzheimer’s disease patients are far less extensive than those found in the brains of Alzheimer’s disease patients.

(B) The developing brain produces a greater number of cells than it will ever use. The extra cells are later destroyed by what biologists call “programmed cell death.”

(C) The procedure that allows scientists to discover the presence of protein deposits during an autopsy is not yet refined enough to ensure detection of the lesions in all patients.

(D) Autopsies have shown that some people lack the chemical necessary for protein deposits to cause brain lesions.

(E) Though most Alzheimer’s disease patients develop the disease when they are in their late fifties to early seventies, the frequency of patients who develop the disease in their forties is on the rise.

答案是D，这题我看的头都晕了。。麻烦分析一下。。


另外，最近复习CR，觉得深陷瓶颈，做题的正确率还是无法提高。。

夏日飘雪

感觉逻辑好难啊。。。有没有比较简便易行的方法呢？

夏日飘雪

16. Investigators concluded that human failure was not responsible for the fatal airplane crash last August, and since that time new and more stringent rules for identifying and reporting mechanical problems have been in effect. That accounts for the fact that reports of airplane mechanical problems have increased in frequency by 50 percent since last August.

Which one of the following is an assumption underlying the argument in the passage?

(A) Airplane travel is still relatively safe, despite the increase in reported mechanical problems.

(B) Mechanical problems in airplanes have increased dramatically since last August.

(C) Mechanical problems in airplanes have not increased by 50 percent since last August.

(D) Airlines are less reluctant to report mechanical problems than they previously were.

(E) Mechanical problems in airplanes have become easier to detect since last August.

答案是C，为什么不可以选E啊？而且我觉得E也可以NOT下削弱结论啊。。。

我要疯了。。以前做对的题目现在反而做错了，而且丝毫没觉得错在哪里。。

evilleo

第一题。从题给条件我们只能推出如果有人发言，那么只有一种可能可能Some Democrat spoke at the convention if he or she was not a senator，但是我们不能肯定一定会有人发言，也就说明我们不能肯定Democrat一定会发言。不能选C

夏日飘雪

第一题。从题给条件我们只能推出如果有人发言，那么只有一种可能可能Some Democrat spoke at the convention if he or she was not a senator，但是我们不能肯定一定会有人发言，也就说明我们不能肯定Democrat一定会发言。不能选C

-- by 会员 evilleo (2010/8/2 22:12:06)

第一句话说了No senator spoke at the convention unless he or she was a Democrat。也就是说如果除非senator是Democrat才发言，这代表senator就不发言吗？我觉得D也不对啊。。

evilleo

第一句话说了No senator spoke at the convention unless he or she was a Democrat。也就是说如果除非senator是Democrat才发言，这确实不能代表senator不发言，因为根据这种情况，如果senator是Democrat的话，senator就发言了。但是看后面那句话， No Democrat both spoke at the convention and was a senator。说明前面那种情况是不存在的。因此可以肯定的是senator没有发言。

jczephyr

段子说海默茨症患者有异常蛋白沉淀造成的brain lesions，又说非海默茨症患者的老年人脑切片发现类似蛋白沉淀，就得结论老年人必得非海默茨症。这样推理，这种蛋白沉淀就是得海默茨症的充分条件了，D说有些人缺乏从蛋白沉淀到brain lesions过程需要的化学物质，没形成brain lesions，也就不得海默茨症了吧。按这题的说法，海默茨症的直接病因是brain lesions，而不是异常蛋白沉淀。如果真是这样，找到一种方法，阻断从异常蛋白沉淀到brain lesions的过程，就有希望治疗海默茨症啦？