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# sharp edged-flakes

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Senior Manager
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07 Jun 2008, 10:40
Set 21, Q 34

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

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Manager
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07 Jun 2008, 10:52
I will go with B..!!!!

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Intern
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07 Jun 2008, 11:02
diehard4 wrote:
I will go with B..!!!!

I am confused between C and E

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08 Jun 2008, 15:49
I think C is the best

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10 Jun 2008, 22:49
mbawaters wrote:
Set 21, Q 34

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

E for me.
Though I am not at all sure

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10 Jun 2008, 23:47
C for me.

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11 Jun 2008, 00:24
mbawaters wrote:
Set 21, Q 34

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

Tricky question

IMO C for this one

what is the OA for this one
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11 Jun 2008, 04:40
C for me as well

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11 Jun 2008, 11:06
mbawaters wrote:
Set 21, Q 34

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

I was stuck between B and C.
C sounds better to me, but I didnt like 'have made stone tools' - as that seems to suggest we still make 'stone tools' to this day.
but, now that I consider B, A could also be a possibility. no need for a past perfect, 'had made' in B - just a simple past 'made'. 'when' properly refers to the date, and..I suppose I can deal with the ambiguous 'it'.

so, my final choice is A!
B, just seems wordy and 'it' does not have a clear referent.
hhmm, now that I think of it

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11 Jun 2008, 11:44
mbawaters wrote:
Set 21, Q 34

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
The use of of "when it is" is redundant. "The earliest date known" would be sufficient to get the point across. Also, to what does "it" refer? The antecedent of "it" is unclear, but this is clearly not the right answer!
This answer includes "had made" and the sentence doesn't need "had". This is past perfect which describes and event that took place and ended in the past.
C. at which humans are known to have made
This is correct because "the earliest date at which" makes sense. Furthermore, "have made" is a proper use of present perfect, which this sentence is. We "know" in the present, and we know humans are to have made something. We know of any event as if it is in the present, so "have made" is present perfect and is correct.
D. that humans are known to be making
"known to be making" is not the proper tense with respect to the rest of the sentence. This verb usage means humans are know to be CURRENTLY making, which is not the point of the sentence.
E. of humans who were known to make
Read the sentence together with the answer: "...the earliest date of humans"? This doesn't make sense. When using "earliest date" it must refer to the date of some event, not date of some thing.

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11 Jun 2008, 11:47
C form e too.

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11 Jun 2008, 11:57
"when" refers to a time and "where" refers to location also past perfect is not needed.

So B & C is rejected. Going with A

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11 Jun 2008, 12:11
1
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I don't think you need "when" in the sentence as in A.

We don't hear people say or write things like this:

The earliest date when he played based was July 7, 1974.

We see something like this:

The earliest date he played baseball was July 7, 1974.

This is a tough SC problem.
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11 Jun 2008, 12:24
1
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mbawaters wrote:
Set 21, Q 34

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

what is "it" refering to in A and B? What is known? so A and B are out
D has serious tense issues since "to be making" means that this action continues till today
E is out since "..date of humans.." is awkward and unidiomatic

C

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11 Jun 2008, 12:48
jallenmorris wrote:
I don't think you need "when" in the sentence as in A.

We don't hear people say or write things like this:

The earliest date when he played based was July 7, 1974.

We see something like this:

The earliest date he played baseball was July 7, 1974.

This is a tough SC problem.

Good explanation!!!
+1 for you
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12 Jun 2008, 09:48
so whats the OA??

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12 Jun 2008, 11:20
I know that C sounds better and is probably the correct answer. But I cant seem to convince myself that 'have made stone tools' is correct here.
present perfect means that something started in the past and is still going on now --> so, here, are we saying that humans are still making stone tools to this day?

is the present perfect, 'have made' used to // '[scientists] have dated' ?

thanks.

jallenmorris wrote:

C. at which humans are known to have made
This is correct because "the earliest date at which" makes sense. Furthermore, "have made" is a proper use of present perfect, which this sentence is. We "know" in the present, and we know humans are to have made something. We know of any event as if it is in the present, so "have made" is present perfect and is correct.

[/quote]

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12 Jun 2008, 11:43
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gmat blows wrote:
I know that C sounds better and is probably the correct answer. But I cant seem to convince myself that 'have made stone tools' is correct here.
present perfect means that something started in the past and is still going on now --> so, here, are we saying that humans are still making stone tools to this day?

is the present perfect, 'have made' used to // '[scientists] have dated' ?

thanks.

jallenmorris wrote:

C. at which humans are known to have made
This is correct because "the earliest date at which" makes sense. Furthermore, "have made" is a proper use of present perfect, which this sentence is. We "know" in the present, and we know humans are to have made something. We know of any event as if it is in the present, so "have made" is present perfect and is correct.

[/quote]

Hi Gmat_Blows,

present perfect is used in conditions where the action is continuing into the present OR if something still holds true.

so both the following are examples

Bush has been president for the last 8 years
The democratic party have known to be holding anti Bush rallies for the last 8 years

now look at the second sentence above, its not that rallies are still going on, but the fact the fact "known to be" is the fact that the present perfect applies to here.

This is the case with our sentence here. "known to have made stone tools" is correct since it is still known (the fact still holds true today)

hope that helps.

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13 Jun 2008, 10:46
thanks - that definitely convinced me! +1

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Re: sharp edged-flakes   [#permalink] 13 Jun 2008, 10:46
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