LSAT 107 – Section 4 – Question 20

LSAT 107 - Section 4 - Question 20

October 1999

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT107 S4 Q20
+LR
Except +Exc
Strengthen +Streng
A
60%
167
B
1%
158
C
1%
155
D
33%
160
E
5%
162
151
161
170
 +Hardest 141.321 +SubsectionEasier

Amphibian populations are declining in numbers worldwide. Not coincidentally, the earth’s ozone layer has been continuously depleted throughout the last 50 years. Atmospheric ozone blocks UV-B, a type of ultraviolet radiation that is continuously produced by the sun, and which can damage genes. Because amphibians lack hair, hide, or feathers to shield them, they are particularly vulnerable to UV-B radiation. In addition, their gelatinous eggs lack the protection of leathery or hard shells. Thus, the primary cause of the declining amphibian population is the depletion of the ozone layer.

Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that the main cause of the declining amphibian population is the depletion of the ozone layer. This is based on the following facts. First, the ozone layer has been continuously depleted over the last 50 years. Second, ozone blocks UV-B, to which amphibians are vulnerable due to their lack of hair/hide/feathres and because their eggs lack leathery/hard shells.

Notable Assumptions
The author assumes there’s no more significant causal factor for the declining amphibian population than the declining ozone layer.

A
Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes.
This tells us that there are other types of radiation blocked by atmospheric ozone. But if these other types don’t damage genes, there’s no reason to think they play a role in damaging amphibians. So, there’s no clear impact.
B
Amphibian populations are declining far more rapidly than are the populations of nonamphibian species whose tissues and eggs have more natural protection from UV-B.
This provides evidence that the lack of protection to UV-B is helping to cause amphibian populations to decline.
C
Atmospheric ozone has been significantly depleted above all the areas of the world in which amphibian populations are declining.
This strengthens the connection betwen ozone depletion and declining amphibian populations.
D
The natural habitat of amphibians has not become smaller over the past century.
This strengthens by eliminating an alternate explanation for the declining amphibian population. If the natural habitat had been getting smaller, that could have been the main reason amphibians are dying off. (D) eliminates this possibility.
E
Amphibian populations have declined continuously for the last 50 years.
Since we’re told the ozone depletion has been occurring “continuously” over the past 50 years, (E) helps strengthen the connection between the declining amphibian population and the depleting ozone.

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LSAT PrepTest 107 Explanations

Section 1 - Logical Reasoning

Section 2 - Reading Comprehension

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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