help?

bigmouse

LSAT-Section16-III-18,23,24
8. In experiments in which certain kinds of bacteria were placed in a generous supply of nutrients, the populations of bacteria grew rapidly, and genetic mutations occurred at random in the populations. These experiments show that all genetic mutation is random.
Which one of the following, if true, enables the conclusion to be properly drawn?
(A) Either all genetic mutations are random or none are random.
(B) The bacteria tested in the experiments were of extremely common forms.
(C) If all genetic mutations in bacteria are random, then all genetic mutations in every other life form arc random also.
(D) The kind of environment in which genetic mutation takes place has no effect on the way genetic mutation occurs.
(E) The nutrients used were the same as those that nourish the bacteria in nature.
answer:A my choice

23. Asbestos, an almost indestructible mineral once installed as building insulation, poses no health risk unless the asbestos is disturbed and asbestos fibers are released into the environment. Since removing asbestos from buildings disturbs it, thereby releasing asbestos fibers, the government should not require removal of all asbestos insulation.
Which one of the following, if true, most strengthens the argument?
(A) Asbestos poses far less risk to health than does smoking, drug and alcohol abuse, improper diet or lack of exercise.
(B) Asbestos can post a health threat to workers who remove it without wearing required protective gear.
(C) Some kinds of asbestos, when disturbed, pose greater health risks than do other kinds.
(D) Asbestos is inevitably disturbed by building renovations or building demolition.
(E) Much of the time, removed asbestos is buried in landfills and forgotten with no guarantee that it will not be disturbed again.
answer:E my choice

When volcanic lava solidifies, it becomes uniformly magnetized in the direction in which the Earth's magnetic field points. There are significant differences in the direction of magnetization among solidified lava flows from different volcanoes that erupted at different times over the past several million years. Therefore, it must be that the direction of the Earth's magnetic field has changed over time. Since lava flows differing by thousands of years in age often have very similar directions of magnetization, the change in the direction of the Earth's magnetic field must take place very gradually over hundreds of thousands of years.
24. The argument that the direction of the Earth's magnetic field has changed over time requires the assumption that
(A) only lava can be used to measure the direction of the Earth's magnetic field as it existed in the distant past
(B) a single volcano can produce lava of differing consistencies during different eruptions
(C) not all solidified lava has changed the direction of its magnetization
(D) there are fewer volcanic eruptions now than there were millions of years ago
(E) as lava flows down the side of a volcano, it picks up magnetized rocks
answer:C my choice:A

merlion

in 8, certain kinds of bacteria,  genetic mutations random->all genetic mutation random
if(a) is not right, there can be some genetic mutations are random, and some not, then the conclusion can not be drawn.

in23 (e), "with no guarantee that it will not be disturbed again", it may mean that removed asbestos will be disturbed again, and removal of all asbestos insulation may pose health risk. So the government should not require removal ...

hope i said nothing wrong

bigmouse

第8题，我觉得还是没理解，答案D为什么不对？

merlion

呀，我也不太清楚，只注意结论中的 all 了。
希望别人可以帮忙解释。

mindfree

8. The argument did not specify "If all genetic mutations in bacteria are random" or not. It only tells you that in that particular experiement, GM are random. To make D the answer, the argument needs an extra assumption that all genetic mutations in bacteria are random.

A is right. Example, Human are either cold-blooded or warm-blooded. Now we find that that Mexicans are warm-blooded, we can conclude that all human beings are warm-blooded.

bigmouse

thank you! mindfree

ecsniffer

24、When volcanic lava solidifies, it becomes uniformly magnetized in the direction in which the Earth’s magnetic field points. There are significant differences in the direction of magnetization among solidified lava flows from different volcanoes that erupted at different times over the past several million years. Therefore, it must be that the direction of the Earth’s magnetic field has changed over time. Since lava flows differing by thousands of years in age often have very similar directions of magnetization, the change in the direction of the Earth’s magnetic field must take place very gradually over hundreds of thousands of years.


The argument that the direction of the Earth’s magnetic field has changed over time requires the assumption that

(A) only lava can be used to measure the direction of the Earth’s magnetic field as it existed in the distant past

(B) a single volcano can produce lava of differing consistencies during different eruptions

(C) not all solidified lava has changed the direction of its magnetization unpredictably

(D) there are fewer volcanic eruptions now than there were millions of years ago


(E) as lava flows down the side of a volcano, it picks up magnetized rocks


the key:C


不理解，谁能给讲讲？

[此贴子已经被作者于2004-3-7 0:19:42编辑过]

weiyu

Principle: 地球磁场方向和固化的岩浆磁场方向一致；固化的岩浆磁场方向在过去几百万年里是变化的，所以地球磁场也随之变化。fficeffice" />

Conclusion: 因为过去几万年中岩浆磁场方向缓慢变化，所以地球磁场在过去几万年中缓慢变化；（你观察到的都是现在的情况）

Assumption: 如果在几万年中，有的岩浆有过几次剧烈的磁场变化，但是几次变化相互抵消导致综合变化不大，那根据Principle地球磁场应当和岩浆磁场一致，那地球磁场就不是change gradually了吧。

    

本人拙见，如有不对，还请ecsniffer多多指正

ecsniffer

thks, weiyu.



Now I have some new opinions. Please check for me!


The question is "The argument that the direction of the Earth’s magnetic field has changed over time requires the assumption that"


this question only refers to the former part of the passage, that is,"When volcanic lava solidifies....Therefore, it must be that the direction of the Earth’s magnetic field has changed over time. "


From the fact that    volcanic lava    becomes uniformly magnetized in the direction in which the Earth’s magnetic field points, the author concluded that the direction of the Earth’s magnetic field     affects that of    magnetization    among    solidified    lava flows, but he ignored the possibility that all solidified lava has changed the direction of its    own magnetization unpredictably. Here, the word "unpredictably" means that the direction of magnetization is changed    beyond the control of the Earth's magnetic field.


so answer is C.


Appreciate more dissusions!


    


    

[此贴子已经被作者于2004-3-7 10:21:16编辑过]

weiyu

thks ecsniffer. I agree with you. Here the change of direction of lava manifests the change of direciton of earth.