请教LSAT-6-III-13,17,23

joywzy

Arguing that there was no trade between Europe and East Asia in the early Middle Ages because there are no written records of such trade is like arguing that the yeti, an apelike creature supposedly existing in the Himalayas, does not exist because there have been no scientifically confirmed sightings. A verifiable sighting of the yeti would prove that the creature does exist, but the absence of sightings cannot prove that it does not.

13. Which one of the following considerations, if true, best counters the argument?

(A) Most of the evidence for the existence of trade between Europe and East Asia in the early Middle Ages is archaeological and therefore does not rely on written records.

(B) Although written records of trade in East Asia in the early Middle Ages survived, there are almost no Europe documents from that period that mention trade at all.

(C) Any trade between Europe and East Asia in the early Middle Ages would necessarily have been of very low volume and would have involved high-priced items, such as precious metals and silk.

(D) There have been no confirmed sightings of the yeti, but there is indirect evidence, such as footprints, which if it is accepted as authentic would establish the yeti's existence.

(E) There are surviving European and East Asian written records from the early Middle Ages that do not mention trade between the two regions but would have been very likely to do so if this trade had existed.

答案:E,E为什么会是削弱呢?

17. Samples from the floor of a rock shelter in Pennsylvania were dated by analyzing the carbon they contained. The dates assigned to samples associated which human activities formed a consistent series, beginning with the present and going back in time, a series that was correlated with the depth from which the samples came. The oldest and deepest sample was dated at 19,650 years before the present, plus or minus 2,400 years. Skeptic, viewing that date of human migration into North America, suggested that the samples could have been contaminated by dissolved "old carbon" carried by percolating groundwater from nearby coal deposits.

Which one of the following considerations, if true, argues most strongly against the suggestion of the skeptics?

(A) No likely mechanism of contamination involving percolating groundwater would have affected the deeper samples from the site without affecting the uppermost sample.

(B) Not every application of the carbon-dating procedure has led to results that have been generally acceptable to scientists.

(C) There is no evidence that people were using coal for fuel at any time when the deepest layer might have been laid down.

(D) No sample in the series, when retested by the carbon-dating procedure, was assigned an earlier date than that assigned to a sample from a layer above it.

(E) No North American site besides the one in Pennsylvania has ever yielded a sample to which the carbon-dating procedure assigned a date that was comparably ancient.

答案:A,不明白A为什么是削弱?

23. Anthony: It has been established that over 80 percent of those who use heirom have a history of having used marijuana. Such evidence would seem to prove that smoking marijuana definitely leads to heroin use.

Judith: Maybe smoking marijuana does lead to heroin use, but it is absurd to thins that citing those statistics proves that it does. After all, 100 percent of the people who take up heroin had a previous history of drinking water.

Judith's reply to Anthony's argument relies on which one of the following argumentative strategies?

(A) offering evidence suggesting that the statistics Anthony cites in support of his conclusion are inaccurate

(B) understanding the credibility of his conclusion by showing that it is a statement from which absurd consequences can be derived

(C) providing an example to show that not everything that promotes heroin use is unsafe

D) demonstrating that Anthony's line of reasoning is flawed by showing such reasoning can lead to clearly false conclusions

(E) calling into question the possibility of ever establishing causal connections solely on the basis of statistical evidence .

答案, 我选了B,不知B/D有什么区别,我用逻辑技巧题时,经常会在两个选项中难以选择,拿不定主意.不知有什么好办法?

谢谢.

mindfree

Have to answer in English.

1. After you finish reading the passage, you should know that the author drew a parallel reasoning between the trade and yeti (a kind of primate I think, or snowman). If No record --> no trade, then no sighting --> no yeti; But a sighting can prove that yeti exists. So there might have been trade, just not on the record. If trade and yeti are not comparable in this regard, the argument is flawed.

E is right in that it states that if there was trade, it would be very likely that the written record will mention it. Therefore, no mention, likely no trade. This is the difference between the case of yeti and that of trade. Yeti is living in area uninhabited by human, so no sighting cannot rule out the possibility of its existence. But there would be record if there was trade.

2. As long as you understand the passage and the choices, the answer stands out itself. The passage says that a series of layers shows the date of huamn presence, from the earliest to present. The deepest represents the earliest and the top the present. Now the critics suspect that the layer was contaminated by coal mine from somewhere else. From this sentecne "The oldest and deepest sample was dated at 19,650 years before the present, plus or minus 2,400 years. Skeptic, viewing that date of human migration into North America, ..." you should know that the skeptics suspect that the deepest layer was contaminated as the history of human might not date back to 19650 years before minus or plus 2400 years. And that is why they suspect that the layer was contaminated by old coal mine, which apparently contained carbon of old age.

Now you should know why A is correct. If the deepest layer is contaminated, the top layer should be contaminated too. But there is no sign of that according to the passage.

3. B is wrong because it is the reasoning of Anthony that leads to absurd conclusion, not his conclusion that leads to an absurd conclsion. Read the choice B again

B. understanding the credibility of his conclusion by showing that it is a statement from which absurd consequences can be derived

joywzy

mindfree,

After reading your explanation several times, I eventually undestand. As u always mention, reading is essential to logic. If i can clear out all the passage and choice , the answer will stand out itself. Admittedly, reading is my biggest obstacle, even in logic.

Thank you very much.