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

soure: preptest1 OA is C

what's wrong with D?

i think you know that we have idiom here..

X, But Y

so using that, I get to know that i need a verb in But clause. So A, B, and E are out.
Out of C and D, I scanned vertically and found that:

that promotes blood and to promote

we need parallelism..and in second half of substance we have, Which prevents clotting.

so in D we have,

to promote clotting --- parallel with prevents clotting
Which is inaccurate...in C we have correct parallelism. Hence, is the answer.

I agree with sunny.jain

The main problem is parallelism

(C) a substance that promotes blood clotting, but does not seriously interfere

X that does Y, but does not Z

(D) which is a substance to promote blood clotting, but does not seriously interfere

X is to Y but does not Z

C is more parallel.

IMO Another problem is that D changes the meaning

option C says that the substance itself promotes blood clotting. On the other hand option D says that the substance is to promote blood clotting. In other words, somebody/something uses the substance to promote blood clotting. The latter is not the intended meaning of the sentence.

It's about getting the right structure between "promote" and "interfere." Promote X but not Y.

Nothing to do with "to promote clotting --- parallel with prevents clotting." You are looking at the wrong parallel structure.

Regards.

Also, as an afterthought, and might be a key indicator, "which" should always modify a noun not a long phrase.

I think here which modifies a noun thromboxane. What do you think it tries to modify?

nah. you're making the wrong comparison.

the meaning of the sentence is:
aspirin blocks X (X is a substance that promotes clotting)
BUT
aspirin does not interfere with the production of Y (Y is a substance that prevents clotting).

in other words, in the correct answer choice, the structure is actually like this:
In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane, a substance that promotes blood clotting, but does not seriously interfere with the production of prostacyclin, which prevents clotting.

so, parallelism is not the key differentiator between (c) and (d).

--

there are two problems i see in (d).

--

problem #1

a substance to promote... is unidiomatic.
the only context in which i can remember "a NOUN to VERB" is a context in which the NOUN is abstract in nature. for instance:
a way to produce goods
a reason to try harder
etc.
note that "substance" is a concrete item; it's not an abstraction like "way" or "reason".

if you're talking about concrete objects, you should replace the infinitive with something else. for instance:
* a substance to promote X (incorrect) --> a substance that promotes X (correct)
* a tool to install the shelves (incorrect) --> a tool with which to install the shelves (correct)

--

problem #2

"which is" is unnecessary and ugly.

if "which is" is followed by a description of something, you should just omit it, producing an appositive modifier:
X, which is a substance... (ugly) --> X, a substance... (better)
Person X, who is the coach of Team Y (ugly) --> Person X, the coach of Team Y (better)

etc.

Thank you very much for the explanation

glad it helped

1# Australian embryologists have found evidence to suggest that (the original wrong word is--evidence that suggests that )the elephant is descended from an aquatic animal and that its trunk originally evolved as a kind of snorkel.

2# In the mid-1920s the Hawthorne Works of the Western Electric Company was the scene of an intensive series of experiments investigating (the wrong options are-- experiments for suggesting and experiments to suggest)the effects that changes in working conditions would have on workers' performance.

3# The largest trade-book publisher in the United States has announced the creation of a new digital imprint division, under which it will publish about 20 purely digital works to be sold online as either electronic books or downloadable copies that can be printed upon purchase.

4#Hydrocarbons, with which fruit flies perfume themselves in species-specific blends, are known to be important in courtship, apparently assisting flies that taste (the wrong counterpart is flies to taste)the hydrocarbons on prospective mates in distinguishing their own species from others.
* all from GMATPrep.

Ron, in above 4, i can pick up the answer without distinguishing between Noun that do/dose and Noun to do.

I know Noun to do is iferior to Noun that do/dose when the Noun is concrete, but it seems that sometimes GAMT do not care the construct --concrete Noun + to do--as in the case of 1# and 3#, rather than 2# and 4#. Ron, could you share your insight about these 4 questions? i will be pleased to hear your opinion.


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* a tool to install the shelves (incorrect) --> a tool with which to install the shelves (correct)

Ron, i am not familiar with the red part; can we write a sentence in this way? i thought that which must be followed a clause when fuctioning as relative pronoun.

_________________
stephen