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Astronomers..

by dadu » Mon Aug 08, 2011 8:52 pm
Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers that the star was created sometime in the seventeenth century - 1670 is often a date that has been plumped for.
(A) Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers
(B) Based on the physical parameters of expanding cloud of stellar debris, astronomers have estimated
(C) Having been based on the physical parameters of expanding cloud of stellar debris, astronomers have estimated
(D) Based on the physical parameters of expanding cloud of stellar debris, astronomers had estimated
(E) Based on the physical parameters of expanding cloud of stellar debris, the estimation by astronomers suggests

Please help.
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by rppala90 » Mon Aug 08, 2011 9:41 pm
E because the estimation was based on the physical properties.
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by GmatKiss » Tue Aug 09, 2011 2:31 am
IMO:B
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by need720+ » Tue Aug 09, 2011 2:37 am
IMO B
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by sl750 » Tue Aug 09, 2011 4:08 am
I would go with B.

The modifier "Based on the physical parameters of expanding cloud of stellar debris" should modify the subject. The pronoun it refers to the star, which is not the subject here

In C, the construction starts with 'Having been' which should be avoided as recommended by the 'experts'
In D, the past perfect tense is wrong as it suggests that the Astronomers made the estimation even before the star was born

In E, the subject (Astronomers) is not being modified
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by kzos » Tue Aug 09, 2011 4:14 am
Agree B it is.

1. I ruled out A due to pronoun issue - it.
2. C and E have diction as well as passive voice issue.
3. Now between B and D. here we are tested on verb tense use. In the sentence - a date that has been plumped for - in the present perfect tense. if we use "had estimated" then it means that estimation happened way way back before ..... I picked B.

---------------had estimated------------was created(A Moment in the past)--------------------The present moment----->

Please correct me if I am wrong.
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by 2299rkt » Tue Aug 09, 2011 5:04 am
IMO E
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by dadu » Wed Aug 10, 2011 2:39 am
OA is E.

As per the explanation, in B, the opening Participial phrase "Based on...." incorrectly modifies "astronomers". The logical meaning of the sentence suggests that the "estimates" were based on the physical parameters of expanding cloud of stellar debris.
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by kzos » Wed Aug 10, 2011 3:02 am
dadu wrote:OA is E.

As per the explanation, in B, the opening Participial phrase "Based on...." incorrectly modifies "astronomers". The logical meaning of the sentence suggests that the "estimates" were based on the physical parameters of expanding cloud of stellar debris.
hmmm .... what is the source of this question. Check the similiar questions in OG12 - #25, #28, and #126.
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by aspirant2011 » Wed Aug 10, 2011 9:10 am
I would go with B, can you please post it to an expert so that we all can be clear on the point which many of us may be missing.......
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by GMATGuruNY » Wed Aug 10, 2011 1:29 pm
dadu wrote:Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers that the star was created sometime in the seventeenth century - 1670 is often a date that has been plumped for.
(A) Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers
(B) Based on the physical parameters of expanding cloud of stellar debris, astronomers have estimated
(C) Having been based on the physical parameters of expanding cloud of stellar debris, astronomers have estimated
(D) Based on the physical parameters of expanding cloud of stellar debris, astronomers had estimated
(E) Based on the physical parameters of expanding cloud of stellar debris, the estimation by astronomers suggests

Please help.
Ignore this SC.
Every answer choice needs to say based on the physical parameters or A cloud of stellar debris.
The sentence can't say THE star unless it's clear which star is being discussed. Exactly which star is THE star?
It is HIGHLY unlikely that the GMAT would end an SC with a preposition (plumped FOR).
Every answer choice contains at least one additional error:

A: it has no clear antecedent. Eliminate A.

B, C, D: Based on seems to modify astronomers. The astronomers were not based on the physical parameters of [an] expanding cloud. Eliminate B, C and D.

E: The sentence can't say THE estimation unless it's clear which estimation is being discussed. Exactly which estimation is THE estimation? Eliminate E.

There is no correct answer here.
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by gmatjeet » Wed Aug 10, 2011 11:00 pm
Apologies to continue this discussion but i have one query:

Why do we need an antecedent for IT in Option A.

Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers that the star was created sometime in the seventeenth century - 1670 is often a date that has been plumped for.

If we remove the modifier "Based on the physical parameters of expanding cloud of stellar debris" - the sentence reads as "It has been estimated......" which is a normal construction requiring no IT antecedent.
Last edited by gmatjeet on Thu Aug 11, 2011 2:53 am, edited 1 time in total.
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by dadu » Thu Aug 11, 2011 12:56 am
GMATGuruNY wrote: Every answer choice needs to say based on the physical parameters or A cloud of stellar debris.
Hi Mitch, could you please explain the above point.

The way I interpret the sentence, some cloud of stellar debris is expanding and based on the
parameters of this expanding clod of debris, some estimation has been done by the Astronomers.

Is my interpretation not correct?

Also, the OA is E. Not sure in the context of this sentence, why we need to know exactly "what" those estimates are. The point of the sentence is that "the estimation suggests something.....".
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by GMATGuruNY » Thu Aug 11, 2011 3:17 am
gmatjeet wrote:
GMATGuruNY wrote:
dadu wrote:Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers that the star was created sometime in the seventeenth century - 1670 is often a date that has been plumped for.
(A) Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers
(B) Based on the physical parameters of expanding cloud of stellar debris, astronomers have estimated
(C) Having been based on the physical parameters of expanding cloud of stellar debris, astronomers have estimated
(D) Based on the physical parameters of expanding cloud of stellar debris, astronomers had estimated
(E) Based on the physical parameters of expanding cloud of stellar debris, the estimation by astronomers suggests

A: it has no clear antecedent. Eliminate A.

Apologies to continue this discussion but i have one query:

Why do we need an antecedent for IT in Option A.

Based on the physical parameters of expanding cloud of stellar debris, it has been estimated by astronomers that the star was created sometime in the seventeenth century - 1670 is often a date that has been plumped for.

If we remove the modifier "Based on the physical parameters of expanding cloud of stellar debris" - the sentence reads as "It has been estimated......" which is a normal construction requiring no IT antecedent.
The structure in A implies that based on modifies it. Since it lacks a clear antecedent, we have no idea what exactly is based on the physical parameters. It must be clear what a modifier is modifying. Eliminate A.
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by GMATGuruNY » Thu Aug 11, 2011 8:03 am
dadu wrote:
GMATGuruNY wrote: Every answer choice needs to say based on the physical parameters or A cloud of stellar debris.
Hi Mitch, could you please explain the above point.

The way I interpret the sentence, some cloud of stellar debris is expanding and based on the
parameters of this expanding clod of debris, some estimation has been done by the Astronomers.

Is my interpretation not correct?

Also, the OA is E. Not sure in the context of this sentence, why we need to know exactly "what" those estimates are. The point of the sentence is that "the estimation suggests something.....".
Please note the phrasing in your post: SOME cloud of stellar debris and THIS expanding cloud of debris. We can't simply say expanding cloud of stellar debris without a preceding word (an, the, this, some, etc.). The sentence must say AN expanding cloud of stellar debris or THE expanding cloud of stellar debris or THIS expanding cloud of stellar debris, etc.

No native speaker of English would ever say expanding cloud of stellar debris without one of these preceding words. The omission of AN is either a typo or an indication that the writer of the SC is not a native speaker of English.

THE estimation by astronomers implies that we already know what is being estimated. But only at the end of the sentence are we told what is being estimated: the year in which the star was created. The GMAT will never say THE estimation unless it's IMMEDIATELY clear what is being estimated.

Same issue with THE star. When I initially read THE star, I actually thought the sentence meant the FIRST star ever created. The GMAT will never say THE star unless it's immediately clear which star is being discussed.
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