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Oxygen-18 is a heavier-than-normal isotope of oxygen. In a

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Director
Joined: 06 Jan 2008
Posts: 547

Kudos [?]: 540 [1], given: 2

Oxygen-18 is a heavier-than-normal isotope of oxygen. In a [#permalink]

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16 Apr 2008, 11:54
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Oxygen-18 is a heavier-than-normal isotope of oxygen. In a rain cloud, water molecules containing oxygen-18 are rarer than water molecules containing normal oxygen. But in rainfall, a higher proportion of all water molecules containing oxygen-18 than of all water molecules containing ordinary oxygen descends to earth. Consequently, scientists were surprised when measurements along the entire route of rain clouds’ passage from above the Atlantic Ocean, the site of their original formation, across the Amazon forests, where it rains almost daily, showed that the oxygen-18 content of each of the clouds remained fairly constant.
19. Which one of the following statements, if true, best helps to resolve the conflict between scientists’ expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds’ oxygen-18 content?
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions.
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them.

Kudos [?]: 540 [1], given: 2

CEO
Joined: 17 May 2007
Posts: 2947

Kudos [?]: 667 [0], given: 210

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16 Apr 2008, 16:35
A for me. Good question +1.
saravalli wrote:
Oxygen-18 is a heavier-than-normal isotope of oxygen. In a rain cloud, water molecules containing oxygen-18 are rarer than water molecules containing normal oxygen. But in rainfall, a higher proportion of all water molecules containing oxygen-18 than of all water molecules containing ordinary oxygen descends to earth [ reasoning 1]. Consequently, scientists were surprised when measurements along the entire route of rain clouds’ passage from above the Atlantic Ocean, the site of their original formation, across the Amazon forests, where it rains almost daily, showed that the oxygen-18 content of each of the clouds remained fairly constant [conclusion].
19. Which one of the following statements, if true, best helps to resolve the conflict between scientists’ expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds’ oxygen-18 content?
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions. [Good]
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them. [trap alert - remember the arguement is all about oxygen-18 not about the replenishment of rain clouds]
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean. Irrelevant
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere. Irrelevant
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them. - Irrelevant

Kudos [?]: 667 [0], given: 210

Director
Joined: 06 Jan 2008
Posts: 547

Kudos [?]: 540 [0], given: 2

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17 Apr 2008, 12:05
OA is B. can we discuss more.

Yesterday ,I took this test in LSAT-CR1000, and I got 17/24. Any comments on my performance?
Time: Oh yaa I took 3 Min for each question.

Kudos [?]: 540 [0], given: 2

CEO
Joined: 17 May 2007
Posts: 2947

Kudos [?]: 667 [1], given: 210

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17 Apr 2008, 16:26
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I narrowed it down to two A and B and sensed that B was a trap - ah well ... wasnt my best day yesterday in terms of CR answers. B does make sense when you think about it

Oh dont worry about the LSAT hit rate. LSAT ones are a lot more convoluted - they provide great reading practice.

Kudos [?]: 667 [1], given: 210

Re: CR-Oxygen   [#permalink] 17 Apr 2008, 16:26
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