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In laboratory rats

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by GMATsid2016 » Tue Nov 15, 2016 9:26 am
In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane, which is a substance that promotes blood clotting, but not seriously interfering with the production of prostacyclin, which prevents clotting.

(A) which is a substance that promotes blood clotting, but not seriously interfering
(B) a substance that promotes blood clotting, but not seriously interfering
(C) a substance that promotes blood clotting, but does not seriously interfere
(D) which is a substance to promote blood clotting, but does not seriously interfere
(E) which is a substance that promotes blood clotting, but not a serious interference


OAC

Please explain each options.
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by ceilidh.erickson » Tue Nov 15, 2016 3:45 pm
This question is testing PARALLELISM.

In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane, which is a substance that promotes blood clotting, but not seriously interfering with the production of prostacyclin, which prevents clotting.

(A) which is a substance that promotes blood clotting, but not seriously interfering
The conjunction "BUT" signals that we need parallelism: ______ but not _______.
The parallel construction would be "... that promotes... but does not interfere..." The word "interfering" is not parallel; it's a present participle, while "promotes" is a tensed verb.

(B) a substance that promotes blood clotting, but not seriously interfering
Same issue as in A. The distinction between "which is a substance..." and "a substance..." is meaningless.

(C) a substance that promotes blood clotting, but does not seriously interfere
Correct! "promotes" and "does not interfere" are parallel, and there are no other errors.

(D) which is a substance to promote blood clotting, but does not seriously interfere
"... to promote... but does not interfere..." is not a parallel construction. We can't have one infinitive and one tensed verb in a parallel list.

(E) which is a substance that promotes blood clotting, but not a serious interference
"that promotes... but not a[n] interference...." is not a parallel construction. We can't have one verb and one action noun in a parallel list.

The answer is C.
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by GMATsid2016 » Wed Nov 16, 2016 8:25 am
ceilidh.erickson wrote:This question is testing PARALLELISM.

In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane, which is a substance that promotes blood clotting, but not seriously interfering with the production of prostacyclin, which prevents clotting.

(A) which is a substance that promotes blood clotting, but not seriously interfering
The conjunction "BUT" signals that we need parallelism: ______ but not _______.
The parallel construction would be "... that promotes... but does not interfere..." The word "interfering" is not parallel; it's a present participle, while "promotes" is a tensed verb.

(B) a substance that promotes blood clotting, but not seriously interfering
Same issue as in A. The distinction between "which is a substance..." and "a substance..." is meaningless.

(C) a substance that promotes blood clotting, but does not seriously interfere
Correct! "promotes" and "does not interfere" are parallel, and there are no other errors.

(D) which is a substance to promote blood clotting, but does not seriously interfere
"... to promote... but does not interfere..." is not a parallel construction. We can't have one infinitive and one tensed verb in a parallel list.

(E) which is a substance that promotes blood clotting, but not a serious interference
"that promotes... but not a[n] interference...." is not a parallel construction. We can't have one verb and one action noun in a parallel list.

The answer is C.
Hello Ceilidh ,

Thanks for your reply.

Can you please also advise that the usage of WHICH is correct?


Thanks,

Sid
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by ceilidh.erickson » Wed Nov 16, 2016 12:56 pm
Either usage would be correct:
...thromboxane, which is a substance that promotes...
...thromboxane, a substance that promotes...

The first would be a modifying dependent clause, the second is a modifying appositive (noun). Both are perfectly grammatically correct. When that's the case, the right answer will almost always be the more concise one - in this case, the appositive.

However, the GMAT will not make you choose between two grammatically correct options based on concision alone.
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