I'm not an expert on SC but here is the logic I used. The Army Corps of Engineers is building a breakwater. The rest of the sentence describes the "breakwater of rocks". The sentence describes the "breakwater of rocks" in four ways. The first two are found in the phrase "that would rise six feet above the waterline and act as a buffer". Here "rise" and "act" are parallel so this is correct. Then the sentence adds two more descriptions of the breakwater. This is found in the phrase "so that it absorbs the energy of crashing waves and protecting the beaches." This is not parallel. We need an answer that parallels "protecting the beaches". "Absorbing" does this.

GMATMadeEasy wrote:In a plan to stop the erosion of East Coast beaches, the Army Corps of Engineers proposed building parallel to shore a breakwater of rocks that would rise six feet above the waterline and act as a buffer, so that it absorbs the energy of crashing waves and protecting the beaches.

(A) act as a buffer, so that it absorbs
(8) act like a buffer so as to absorb
(C) act as a buffer, absorbing
(D) acting as a buffer, absorbing
(E) acting like a buffer, absorb

OA is C .

Question : What and how the adverbial modifier "absorbing..." in answer choice C modfies ? Subject of the clause is "the Army Corps of Engineers " and action is "proposed" .None seems to be modified by absobring.

ing modifiers modify the entire preceding clause and are attributed to the subject of the preceding clause. Therefore, absorbing here modifies the entire preceding clause.

Further, since the non-underlined portion contains "and protecting the beaches" - We need to use absorbing to maintain the parallelism. Thus we are down to C and D; D is just awkward.

GMATMadeEasy wrote: Question : What and how the adverbial modifier "absorbing..." in answer choice C modfies ? Subject of the clause is "the Army Corps of Engineers " and action is "proposed" .None seems to be modified by absobring.

Ah! You got caught up in the jargon there!

By definition, an adverbial modifier modifies a verb, an adjective or another adverb. The subject is invariably a noun, so an adverbial modifier can never modify the subject.

Look at the sentence C -
In a plan to stop the erosion of East Coast beaches, the Army Corps of Engineers proposed building parallel to shore a breakwater of rocks that would rise six feet above the waterline and act as a buffer, absorbing the energy of crashing waves and protecting the beaches.

Simplify -
Engineers proposed building A that would rise six feet above B and act as a buffer, absorbing the energy of crashing waves and protecting the beaches.

Ask the question - How would A act as a buffer?
Answer - By absorbing the energy of crashing waves and protecting the beaches.

The modifier is telling us more about how would A act. So, absorbing the energy of crashing waves and protecting the beaches. is modifying the verb act and is thus an adverbial modifier.

niksworth wrote:

GMATMadeEasy wrote: Question : What and how the adverbial modifier "absorbing..." in answer choice C modfies ? Subject of the clause is "the Army Corps of Engineers " and action is "proposed" .None seems to be modified by absobring.

Ah! You got caught up in the jargon there!

By definition, an adverbial modifier modifies a verb, an adjective or another adverb. The subject is invariably a noun, so an adverbial modifier can never modify the subject.

Look at the sentence C -
In a plan to stop the erosion of East Coast beaches, the Army Corps of Engineers proposed building parallel to shore a breakwater of rocks that would rise six feet above the waterline and act as a buffer, absorbing the energy of crashing waves and protecting the beaches.

Simplify -
Engineers proposed building A that would rise six feet above B and act as a buffer, absorbing the energy of crashing waves and protecting the beaches.

Ask the question - How would A act as a buffer?
Answer - By absorbing the energy of crashing waves and protecting the beaches.

The modifier is telling us more about how would A act. So, absorbing the energy of crashing waves and protecting the beaches. is modifying the verb act and is thus an adverbial modifier.

I don't really want to argue with you, niksworth, because you are consistently really fantastic on the Verbal side -- I really admire your knowledge and your posting. It seems to me, though, that "absorbing . . " is just a plain old participial phrase modifying "buffer". Participles are verbal adjectives; participial phrases can be replaced by non-restrictive relative clauses ("which would absorb . . .").

Of course, we'd probably still be debating what a COMMA + WHICH phrase was modifying in the same position.

Ah! Jim, you have a point there.

The reason why I did not consider this phrase a participle modifying buffer is the comma. Had the comma not been there, undoubtedly the phrase would have been modified buffer.

comma+verbing on the other hand, often acts adverbially. Or am I wrong? Thoughts?