Scientists have dated sharp-edged flakes of stone found in : GMAT Sentence Correction (SC)
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# Scientists have dated sharp-edged flakes of stone found in

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Intern
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Scientists have dated sharp-edged flakes of stone found in [#permalink]

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28 Aug 2010, 13:39
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35% (medium)

Question Stats:

62% (01:59) correct 38% (01:12) wrong based on 253 sessions

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Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments
of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million
years ago, pushing back by more than 150,000 years the earliest date when it is
stone tools.
A. when it is known that humans made
C. at which humans are known to have made
D. that humans are known to be making
E. of humans who were known to make
[Reveal] Spoiler: OA
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink]

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28 Aug 2010, 22:16
C is correct.

Given : Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million
years ago, pushing back by more than 150,000 years the earliest date when it is
stone tools.

I simplified the sentence to:

Scientists have dated tool2 to between x and y yrs ago, pushing back z yrs the date when it is known that humans made tools.

A. when it is known that humans made - un-referenced pronoun "it" - wrong
B. at which it is known that humans had made - wrong
C. at which humans are known to have made - Correct
D. that humans are known to be making - wrong
E. of humans who were known to make - wrong
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink]

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29 Aug 2010, 15:56
Please underline the question. It's really difficult to understand the question without underline!.

Thank you.
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink]

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29 Aug 2010, 16:06
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink]

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29 Aug 2010, 16:19
kissthegmat wrote:
Please underline the question. It's really difficult to understand the question without underline!.

Thank you.

The answer option A is always the underlined part from the given sentence. I don't think its necessary to underline it.
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink]

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15 Mar 2016, 04:45
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iDisappear wrote:
Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments
of a dry riverbed in the Afar region of Ethiopia to between 2.52 and 2.60 million
years ago, pushing back by more than 150,000 years the earliest date when it is
known that humans made stone tools.
A. when it is known that humans made
C. at which humans are known to have made
D. that humans are known to be making
E. of humans who were known to make

Here 'when' is used as an adverb after an expression of time to mean 'at which'.
'Sunday is the only day when I can relax.
The action 'relax' takes place on Sunday.
In the problem the action 'is known' takes place at a particular point of time in the past. It is incorrect. The correct action is 'humans made stone tools'.
Therefore, I think it is correct to say 'when humans made stone tools', or 'when human are known to have made stone tools'.
Both the structures are absent in the options.
But we can replace 'when' with 'at which'.
So, we have the correct option C
Re: Scientists have dated sharp-edged flakes of stone found in   [#permalink] 15 Mar 2016, 04:45
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