PREP 老版29 CR 谢谢大家

fay009

29. (30663-!-item-!-188;#058&005676)
To prevent harbor porpoises from getting tangled in its nets and suffocating, a fishing company installed acoustic alarms on all its boats that fish in waters off Massachusetts.  The sound emitted temporarily disorients the porpoises and frightens them away.  Since the installation of the alarms, the average number of porpoises caught in the company's nets has dropped from eight to one per month.  The alarms, therefore, are saving the lives of harbor porpoises in those waters.
Which of the following is an assumption on which the argument depends?
(A) The use of acoustic alarms increases the number of commercial fish caught by the fishing company's boats.
(B) When disoriented, harbor porpoises are not significantly more likely to be killed by other boats.
(C) Environmentalists advocate the use of acoustic alarms as a means of protecting the harbor porpoise population.
(D) The alarms were installed at the time of year when harbor porpoises are most plentiful in the Massachusetts waters.
(E) The cost of installing acoustic alarms on fishing boats is less than the cost of repairing nets damaged by harbor porpoises.
答案是B。我也认同B。想知道D为什么不对。
如果这个数据是在porpoises很少的时候得到的，那很可能会从8减少到1，而不是因为alarms啊。

coolhaoming

问假设的题可以将假设否定，如果否定后削弱题干，则是正解。

B：否定后显然削弱题干。

D：题干中说the average number of porpoises caught in the company's nets has dropped from eight to one per month，即每月抓到的平均数从8降到了1.  
D说在海豚最多的时候安装，那么数量从8降到了1正说明有效果。如果是在最少的时候安装，也说明有效果。楼主是不是这个意思：在最多的时候安装，后来海豚越来越少，因此补到的也变少了。其实这是有可能的。但是相对于B还是不够好。
另外我感觉假设就是根据前提来推理，D个人感觉不太像前提，呵呵~
请NN指教

fay009

呃~我的意思是，如果在少的时候装，数量减少了，说明这个数量减少不一定因为alarm，所以应该还是在多的时候装才能成为前提~~~

切尔西

题目中没有出现 most plentiful，答案中出现了就肯定不对的

coolhaoming

如果在少了的时候装了，要看和什么时候比了，如果和海豚数量少的季节比，捕捉上来的少了，说明这个装置有用。如果和海豚数量多的季节比，捕捉上来的少了，不能说明这个装置有用。确实这样想D有一定道理，是题干中没有这样的意思，那句话读读感觉还是和安装前后比，应该将海豚数量变化的因素已经考虑进去了。而且相对于B还是太不明显了

fay009

题目中没有出现 most plentiful，答案中出现了就肯定不对的

-- by 会员 切尔西 (2010/3/28 23:39:22)

这个说法未免武断了吧

ShaneLiu

这道题我跟LZ有同样的疑惑，顶上去，求牛牛指点。D为什么错了？

sure6

(B) When disoriented, harbor porpoises are not significantly more likely to be killed by other boats.(not 去掉--?当被迷惑了,海豚更容易被其他船只撞上,更死得快--?驳斥了文章:迷惑使得它们被吓走-从而保护了海豚)

sure6

(B) When disoriented, harbor porpoises are not significantly more likely to be killed by other boats.(not 去掉--?当被迷惑了,海豚更容易被其他船只撞上,更死得快--?驳斥了文章:迷惑使得它们被吓走-从而保护了海豚)

sure6

(B) When disoriented, harbor porpoises are not significantly more likely to be killed by other boats.(not 去掉--?当被迷惑了,海豚更容易被其他船只撞上,更死得快--?驳斥了文章:迷惑使得它们被吓走-从而保护了海豚)