Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.

A. Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.

B. Nearly 99 percent of five hundred million different species of living creatures that appeared on Earth have vanished.

C. Vanished are nearly 99 percent of the five hundred million different species of living creatures that appeared on Earth.

D. Of five hundred million different species of living creatures that have appeared on Earth, nearly 99 percent of them have vanished.

E. Of the five hundred million different species of living creatures that have appeared on Earth, nearly 99 percent have vanished.

I got the right answer my doubt is just that in A is 'them' ambiguous?
I think it can point to 'species' and 'creatures'. Am I right? please explain.

GMATGuruNY wrote:

Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.

A. Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.

B. Nearly 99 percent of five hundred million different species of living creatures that appeared on Earth have vanished.

C. Vanished are nearly 99 percent of the five hundred million different species of living creatures that appeared on Earth.

D. Of five hundred million different species of living creatures that have appeared on Earth, nearly 99 percent of them have vanished.

E. Of the five hundred million different species of living creatures that have appeared on Earth, nearly 99 percent have vanished.

A: Different species have appeared, nearly 99 percent of them vanishing.
Here, the modifier in red implies that nearly 99 percent of the different species were VANISHING when they APPEARED -- a nonsensical meaning.
Eliminate A.

In B and C, appeared (past) implies that the species were NO LONGER ON EARTH when they vanished -- a nonsensical meaning.
Eliminate B and C.

In D, of five hundred different million species and of them are redundant.
Eliminate D.

The correct answer is E.

I got the right answer my doubt is just that in A is 'them' ambiguous?
I think it can point to 'species' and 'creatures'. Am I right? please explain.

It seems clear in A that them is intended to refer to subject of the preceding clause (five hundred different million species).
That said, the OA avoids this issue by omitting them and thus is a better answer choice.

akash singhal wrote:

GMATGuruNY wrote:

Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.

A. Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.

I meant that can pronoun have their antecedent in "prepositional phrases","additive phrases" or other non-restrictive clauses.
I always confuse in such pronoun-antecedent errors. Can you explain with some examples?

Answer choice A:
Five hundred million different species of living creatures have appeared on Earth, nearly 99 percent of them vanishing.
An OA from GMAC:
An overwhelming proportion of women work, many of them in middle management.
These two answer choices employ a similar structure, as illustrated by the portions in red.
Since the usage of them is considered unambiguous in the OA, we should deem its usage unambiguous in answer choice A.

When evaluating a pronoun for ambiguity, we must rely not only on structure but also on context.
In answer choice A, context makes it clear that them is intended to refer to five hundred million different species.

You are correct that a pronoun can serve to refer to the object of a preposition.
For examples, please revisit my posts here:
https://www.beatthegmat.com/parallel-str ... 83199.html