Ground Level

pradeepspanchal wrote:At ground level, ozone is a harmful pollutant, but in the stratosphere it shields the Earth from the most biologically harmful radiation emitted by the Sun, radiation in the ultraviolet band of the spectrum.
(A) in the stratosphere
(B) in the stratosphere, in which
(C) it is in the stratosphere in which
(D) in the stratosphere where
(E) it is in the stratosphere and

I was confused betwee B and D , and picked D becuase it is short . my reasoning ; where and in which are replaceable and where correctly specify the location.

OA A
Please suggest the POE and is in which / where changes meaning here or some other reason

the problem with both B and D is that they leave the rest of the sentence as a fragment with no main verb.
the conjunction "but" opens a new clause, which needs its own subject and verb. In the original sentence, the subject is the pronoun "it' (referring to the Ozone), and the verb is "shields". The sentence's point is that at Ground level, Ozone is A, but in the stratosphere, Ozone is B.

In B and D, the pronouns "which" and "where" signal the beginning of a sub-clause, or relative clause. Think of these as an enclosed bubble - a sentence within a sentence. Any subject and verb following "in which" or "where" are now part of the relative clause, and NOT part of the main clause following "but". Thus, the main clause is left without a main subject or verb:

in B: "...but in the stratosphere, in which it shields the earth....," what? after we skip the "enclosed bubble" of the relative clause, we're looking for some continuation of the main clause. what happens n the stratosphere? the sentence leaves us hanging.
an example which would correct B: "but in the stratosphere, in which it shields...., Ozone is beneficial."
the same thing happens with D: the addition of "where" encloses the subject and verb "it shields" in a sub-clause, leaving the "but" without a main clause to continue it.
C is long and has the same problem ("which" at the end)
E is grammatically correct, but doesn't improve on A - it adds the redundant "it is in the stratosphere" - merely stating that the Ozone exists in the stratosphere, which is already implied by the main sentence.

I think that when you first read A, you found nothing wrong with it, but chose some other answer choice just because you felt that "there has to be some error in the original sentence". If that is the case, remember that A has as much chance as being the correct answer as any of the other answer choices. Statistically, the original sentence is correct 20% of the time in GMAT SC questions.

Many Thank Geva for great explanation .

cannot agree more . correct answer has to be A.

Hi Geva

Thanks for pointing out the sentence fragment issue in the sentence. I actauuly didnt read after seeing that D fits here gramatically.

I rejected A because i didnt find a "," after the stratosphere and i think it should be there as you have pointed in your example. below in your explanation.

Should i consider this a typo or this can really stand as a sentence without a comma.

Geva@MasterGMAT wrote:

pradeepspanchal wrote:At ground level, ozone is a harmful pollutant, but in the stratosphere it shields the Earth from the most biologically harmful radiation emitted by the Sun, radiation in the ultraviolet band of the spectrum.
(A) in the stratosphere
(B) in the stratosphere, in which
(C) it is in the stratosphere in which
(D) in the stratosphere where
(E) it is in the stratosphere and

I was confused betwee B and D , and picked D becuase it is short . my reasoning ; where and in which are replaceable and where correctly specify the location.

OA A
Please suggest the POE and is in which / where changes meaning here or some other reason

the problem with both B and D is that they leave the rest of the sentence as a fragment with no main verb.
the conjunction "but" opens a new clause, which needs its own subject and verb. In the original sentence, the subject is the pronoun "it' (referring to the Ozone), and the verb is "shields". The sentence's point is that at Ground level, Ozone is A, but in the stratosphere, Ozone is B.

In B and D, the pronouns "which" and "where" signal the beginning of a sub-clause, or relative clause. Think of these as an enclosed bubble - a sentence within a sentence. Any subject and verb following "in which" or "where" are now part of the relative clause, and NOT part of the main clause following "but". Thus, the main clause is left without a main subject or verb:

in B: "...but in the stratosphere, in which it shields the earth....," what? after we skip the "enclosed bubble" of the relative clause, we're looking for some continuation of the main clause. what happens n the stratosphere? the sentence leaves us hanging.
an example which would correct B: "but in the stratosphere, in which it shields...., Ozone is beneficial."
the same thing happens with D: the addition of "where" encloses the subject and verb "it shields" in a sub-clause, leaving the "but" without a main clause to continue it.
C is long and has the same problem ("which" at the end)
E is grammatically correct, but doesn't improve on A - it adds the redundant "it is in the stratosphere" - merely stating that the Ozone exists in the stratosphere, which is already implied by the main sentence.

I think that when you first read A, you found nothing wrong with it, but chose some other answer choice just because you felt that "there has to be some error in the original sentence". If that is the case, remember that A has as much chance as being the correct answer as any of the other answer choices. Statistically, the original sentence is correct 20% of the time in GMAT SC questions.