Sentence Correction

Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's).

A. acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate
B. acting as a global thermostat and thus keeping Earth either from burning up or freezing over, while also accelerating
C. act as a global thermostat and thus keep Earth from either burning up or freezing over, while also accelerating
D. they act as a global thermostat that thus keeps Earth either from burning up or freezing over, even though it also accelerates
E. they act as a global thermostat to thus keep Earth from either burning up or freezing over, but they also accelerate

OA: A

My doubt is regarding choice A. Here the by the intended meaning the modifier 'acting ........ over' modifies the previous clause but isn't it ambiguous as it can also modify the following clause.

Are these kind of construction acceptable in GMAT ?

As an analogy citing OG12#3:

Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, until almost 1900, scholars and critics did not begin seriously to study traditional Native American poetry in native languages.

Here OG says 'until almost 1900' is ambiguous as it can modify either preceding or following clause.

sui generis wrote:Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's).

A. acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate
B. acting as a global thermostat and thus keeping Earth either from burning up or freezing over, while also accelerating
C. act as a global thermostat and thus keep Earth from either burning up or freezing over, while also accelerating
D. they act as a global thermostat that thus keeps Earth either from burning up or freezing over, even though it also accelerates
E. they act as a global thermostat to thus keep Earth from either burning up or freezing over, but they also accelerate

OA: A

My doubt is regarding choice A. Here the by the intended meaning the modifier 'acting ........ over' modifies the previous clause but isn't it ambiguous as it can also modify the following clause.

Are these kind of construction acceptable in GMAT ?

As an analogy citing OG12#3:

Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, until almost 1900, scholars and critics did not begin seriously to study traditional Native American poetry in native languages.

Here OG says 'until almost 1900' is ambiguous as it can modify either preceding or following clause.

Not all modifiers are the same.

When a PREPOSITIONAL modifier is inserted between two clauses, a reader might struggle to determine which action -- the PRECEDING ACTION or the FOLLOWING ACTION -- is being modified.
In SC3 of the OG12, it is unclear whether poets HAD PRETENDED until almost 1900 or scholars and critics DID NOT BEGIN until almost 1900.

But COMMA + VERBing modifies the nearest PRECEDING action.
This is the DEFAULT interpretation.
Thus, in the OA to the GMATPrep sentence, it is crystal clear that acting and keeping modify how the ice particles reflect and absorb: as the ice particles REFLECT and ABSORB solar radiation, they are at the same time ACTING as a global thermostat and thus KEEPING the earth from either burning up or freezing over.

Thanks for the prompt reply and for clearing the doubt.

GMATGuruNY wrote:

sui generis wrote:Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's).

A. acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate
B. acting as a global thermostat and thus keeping Earth either from burning up or freezing over, while also accelerating
C. act as a global thermostat and thus keep Earth from either burning up or freezing over, while also accelerating
D. they act as a global thermostat that thus keeps Earth either from burning up or freezing over, even though it also accelerates
E. they act as a global thermostat to thus keep Earth from either burning up or freezing over, but they also accelerate

OA: A

But COMMA + VERBing modifies the nearest PRECEDING action.
This is the DEFAULT interpretation.
Thus, in the OA to the GMATPrep sentence, it is crystal clear that acting and keeping modify how the ice particles reflect and absorb: as the ice particles REFLECT and ABSORB solar radiation, they are at the same time ACTING as a global thermostat and thus KEEPING the earth from either burning up or freezing over.

Hi GMATGuruNY - could you please shed some light that why it'd be wrong here to interpret that COMMA + VERBing modifies the nearest PRECEDING action of the preceding ALTHOUGH-clause ?

RBBmba@2014 wrote:

GMATGuruNY wrote:

sui generis wrote:Although ice particles in the upper atmosphere benefit Earth in that they reflect and absorb solar radiation, acting as a global thermostat and thus keeping Earth from either burning up or freezing over, they also accelerate the destruction of the ozone layer by reacting with chlorofluorocarbons (CFC's).

But COMMA + VERBing modifies the nearest PRECEDING action.
This is the DEFAULT interpretation.
Thus, in the OA to the GMATPrep sentence, it is crystal clear that acting and keeping modify how the ice particles reflect and absorb: as the ice particles REFLECT and ABSORB solar radiation, they are at the same time ACTING as a global thermostat and thus KEEPING the earth from either burning up or freezing over.

Hi GMATGuruNY - could you please shed some light that why it'd be wrong here to interpret that COMMA + VERBing modifies the nearest PRECEDING action of the preceding ALTHOUGH-clause ?

The COMMA + VERBing modifier DOES serve to modify the nearest preceding actions in the preceding although-clause.
As I stated in my post, COMMA + acting is an action that happens at the same time as the ice particles REFLECT and ABSORB -- the nearest preceding actions in the introductory although-clause.

Got you!

But still has a doubt that why and how it'd be wrong here to interpret that the VERBing modifies the nearest action of the following Clause starting with the pronoun THEY ? (Because, I guess, COMMA appears by default after an ALTHOUGH-clause. So, COMMA here is not REALLY associated with the construction of the following VERBing modifier and thus the VERBing modifier appears to be at the beginning of the second IC starting with the pronoun THEY and can modify the nearest action in the FOLLOWING clause!)

Isn't the action/main Verb in the second IC --accelerate-- ALSO the nearest action to the VERBing modifier ?

RBBmba@2014 wrote:Got you!

But still has a doubt that why and how it'd be wrong here to interpret that the VERBing modifies the nearest action of the following Clause starting with the pronoun THEY ? (Because, I guess, COMMA appears by default after an ALTHOUGH-clause. So, COMMA here is not REALLY associated with the construction of the following VERBing modifier and thus the VERBing modifier appears to be at the beginning of the second IC starting with the pronoun THEY and can modify the nearest action in the FOLLOWING clause!)

Isn't the action/main Verb in the second IC --accelerate-- ALSO the nearest action to the VERBing modifier ?

A VERBing modifier immediately preceded by a comma serves to express an action concurrent with the nearest PRECEDING verb.
Even if the comma serves an additional function -- such as setting off an introductory although-clause -- this rule still applies.