GMAT OG 2019 Normally a bone becomes fossilized

[BFR]

Normally a bone becomes fossilized through the action of groundwater, which permeates the bone, washes away its organic components, and replaces them with minerals.
A. which permeates the bone, washes away its organic components, and replaces them
B. which permeates the bone, washes away its organic components, and those are replaced
C. which permeates the bone, washing away its organic components, to be replaced
D. permeating the bone, washing away its organic components, to be replaced
E. permeating the bone, washing away its organic components and replacing them

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Hello Everyone!

It looks like we're dealing with a list here, and we know that means one thing: parallelism! Any time you see a list on the GMAT, the first thing you should always do is make sure each item is written using parallel structure!

Let's see how each answer holds up:

(A) which permeates the bone, washes away its organic components, and replaces them --> CORRECT
(B) which permeates the bone, washes away its organic components, and those are replaced --> INCORRECT
(C) which permeates the bone, washing away its organic components, to be replaced --> INCORRECT
(D) permeating the bone, washing away its organic components, to be replaced --> INCORRECT

(E) permeating the bone, washing away its organic components and replacing them --> INCORRECT

So why is E incorrect, even though it uses parallel structure? The GMAT requires the use of the serial comma (aka the Oxford comma) for the last item in a list of 3+ items. Answer E doesn't use a serial comma, so it's wrong.


Don't study for the GMAT. Train for it.

[Terry@ThePrincetonReview]

While it is true that choice E lacks the serial ("Oxford") comma between the parallel items in the list, in my experience the GMAT will never make such a fine point the SOLE reason for eliminating an answer choice. There must be a more substantial reason for eliminating the answer choice. Here the reason is that the participles (permeating ... washing ... replacing) grammatically modify NOT groundwater but the subject of the sentence, bone. But the sentence's logic demands that these participles modify groundwater, so the result is nonsensical.

Here's a similar example where the connection between the participle and the subject modified is clearer: The soccer team has a complicated relationship with its fans, encouraging their support but fearing their fanaticism. The participles encouraging and fearing clearly modify the subject soccer team, not the object fans.

Now take the following example: The forager walked through a forest resounding with the calls of songbirds. The participle resounding modifies the object forest, both logically and grammatically. That's because there is no comma between forest and resounding. If this sentence had a comma after forest - The forager walked through a forest, resounding with the calls of songbirds - the result would be nonsense, because then resounding would have to modify the subject, the hunter.

[lllunix]

Thanks! It's very helpful!