My take-
Premise - Amphibian populations are declining in numbers worldwide.
Premise - Earth's ozone layer has been continuously depleted throughout the last 50 years.
Premise - Atmospheric ozone blocks UV-B, a type of ultraviolet radiation that is continuously produced by the sun, and which can damage genes.
Premise - Amphibians lack hair, hide, or feathers to shield them, they are particularly vulnerable to UV-B radiation.
Additional Premise - In addition, their gelatinous eggs lack the protection of leathery or hard shells.
Conclusion - Thus, the primary cause of the declining amphibian population is the depletion of the ozone layer.
Look for 4 strengtheners.
A - UV-B damages genes, is already stated, A, if true, is like a additional premise which persuades to bolster the argument.
B - Compares Amphibian to nonamphibian species with natural protection from UV-B, if this is true then certainly Amphibian eggs don't have benefit of the egg shell, strengthens.
C - Conclusion states that ozone layer is the cause of population depletion, this statement sites this and gives additional information, strengthens.
D - No effect. This statement does not have any impact on the conclusion or the argument as a whole, if added to the stimulus. Correct.
E - Earth's ozone has depleted continuously from past 50 years and at the same time amphibian population has declined, conclusion claims this, strengthens.

IMO D

Agree with the explanation by beat_Gmat_09.

A B C and E all strengthening the conclusion.

nipunkathuria wrote: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.
Each of the following, if true, would strengthen the
argument EXCEPT:
(A) Of the various types of radiation blocked by
atmospheric ozone, UV-B is the only type
that can damage genes.
(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.
(C) Atmospheric ozone has been significantly
depleted above all the areas of the world in
which amphibian populations are declining.
(D) The natural habitat of amphibians has not
become smaller over the past century.
(E) Amphibian populations have declined
continuously for the last 50 years.



Plz explain with reasons...
OA Soon...
Source : LSAT LR Bible

Amphibians have been decreasing their numbers for a reason : BV.
now we will have to find an answer choice which is weaken the reason above or out of scope.
D is good answer choice. the CR saying that amphibians are decreasing while D saying that its habitat has not become smaller = its becoming huger than ever in the numbers =the Amphibians are not decreasing... theyre actually increasing