This is from GMAT Prep:

While studying the genetic makeup of corn, a new class of mutant genes was discovered by Barbara McClintock, a discovery which led to greater understanding of cell differentiation.

A) a new class of mutant genes was discovered by Barbara McClintock, a discovery which led

b) a new class of mutant genes in corn were discovered by Barbara McClintock, leading

c) Barbara McClintock discovered a new class of mutant genes, and it led

d) Barbara McClintock discovered a new class of mutant genes, a discovery that led

e) Barbara McClintock, who discovered a new class of mutant genes, leading

I was able to eliminate answer choices A and B because the opening phrase modified Barbara. I was also able to eliminate answer choice E because the sentence wouldn't have a verb. I thought answer choice D (which is correct) had some repetition in it since it mentions discovery twice. I chose answer choice C. I don't understand why C is incorrect. Please help!

Between C and D:

C has an 'it' which does not have a clear antecedent. In other words what does 'it' refer to?

"discovery", "new class" or "corn".. ---Thus Ambiguous..

Always be wary of 'it'

the issue is not ambiguity -- remember that ambiguity is NOT a reliable criterion on which to eliminate.
(see here:
post40400.html#p40400)

rather, the problem is that the pronoun in this case is just flat-out incorrect -- neither "new class" or "corn" makes sense if substituted for the pronoun. remember, the sentence has to make LITERAL SENSE if you SUBSTITUTE the antecedent into the location of the pronoun.

if you ask yourself, VERY LITERALLY, "exactly what led to this greater understanding?", then you'll find that the answer is neither the new class nor the corn -- both of those are inanimate objects, which by themselves can't contribute to human understanding.
the exact thing that led to this greater understanding was the discovery described in the sentence; hence the wording of the correct answer.

--

if you didn't like the phrasing of the correct answer, then you probably aren't as comfortable as you should be with ABSTRACT NOUN APPOSITIVES.
for a short description, with examples, see here:
http://www.beatthegmat.com/sc-with-surf ... tml#209928

_________________
Being well-dressed gives a feeling of inward tranquillity [that] religion is powerless to bestow.
C.F. Forbes

Glad Ron's excellent answer helped.

So what is the answer to this question?

The correct answer is D.

_________________
Joe Lucero
Manhattan GMAT Instructor