Source : GmatPrep Test 1

A new genetically engineered papaya was produced not by seed companies who have been motivated by profit, which was the case with most genetically modified crops previously approved for commercial use, but university and United States Department of Agriculture researchers who allowed growers to use it free of charge.

A) produced not by seed companies who have been motivated by profit, which was the case with most genetically modified crops previously approved for commercial use, but

B) produced not by profit-motivated seed companies, the case with most genetically modified crops previously approved for commercial use, but

C) produced not by profit-motivated seed companies, as was the case with most genetically modified crops previously approved for commercial use, but by

D) not produced by profit-motivated seed companies, which was the case with most genetically modified crops previously approved for commercial use, but was produced by

E) not produced by seed companies who have been motivated by profit, the case with most genetically modified crops previously approved for commercial use, but by


I could eliminate A, B and E because in
A) not by X, but Y are not parallel
B) same issue as above
E) not produced by X, but Y are not parallel

Why is C a better construct than D ? Is there a quick way to identify the difference between C & D?

In Choice "C" Not "X" but "Y" both X="by profit-motivated seed companies......" and Y="by........" are parallel.
C) produced not by profit-motivated seed companies, as was the case with most genetically modified crops previously approved for commercial use, but by

In Choice "D" this parallelism is violated as X="produces by...." but Y="was produces by..."
D) not produced by profit-motivated seed companies, which was the case with most genetically modified crops previously approved for commercial use, but was produced by

Thanks

the major reason for eliminating choice d is its improper use of the word 'which'.

the gmat follows a hard and fast rule about the use of relative pronouns (such as which) when set off by commas: they must have a noun referent, which must be located immediately prior to the comma. the gmat does not allow 'which' to refer to an entire clause (as it attempts to do here), much to the chagrin of common english speakers who use 'which' in this way on a regular basis.**

in other words: the gmat's rules for 'which' would require it to stand for 'seed companies' in choice d. not only is that logically absurd, but it doesn't even exhibit proper subject-verb agreement ('companies' doesn't agree with 'was').

note by contrast, that the word 'as' is properly used with entire clauses, as is done in choice c.

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there's also the more minor, but by no means negligible, issue of wordiness: choice c ('not by X but by Y') makes the parallel construction much more concise than does choice d ('was not produced by X but was produced by Y').

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**nb: the gmat violates this rule several times in its discussion of problems, but never violates it in the problems themselves. if you look, you'll notice that the discussion sections seem to be held to much lower standards of grammar than the actual problems; therefore, only pay attention to the gmat's rules of grammar as exhibited in actual problems, not in peripheral discussion.