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# Scientists have dated sharp-edged flakes of stone found in

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Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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Updated on: 23 Oct 2017, 05:47
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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 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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Originally posted by alimad on 03 Sep 2007, 20:47.
Last edited by hazelnut on 23 Oct 2017, 05:47, edited 2 times in total.
Edited the question.
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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04 Dec 2012, 11:59
31
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kuttingchai wrote:
I was not able to decide between A & C.
Can any1 explain the though process behind answering this question?

I'm happy to help with this.

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

The funny thing here is that (A) is more or less grammatically correct, but illogical. This is what is so tricky about GMAT SC --- it's not enough to be analyzing at the level of grammar. We have to take logic into account.

What the sentence is trying to say ----- (a) humans made tools 2.6 Mya, and (b) right now, we know this to be the case. There are two actions, happening at different times --- the tool making (2.6 Mya) and the knowing about the tool-making (right now).

Look at thhe grammatical structure in (A).
.... the earliest date when it is known that humans made stone tools.
What precisely is happening at that "when"-time? Is it the knowing or the making? Technically, the clause that immediately follows "when" is "it is known", so grammatically, this would suggest the knowing happened at this "when"-time, 2.6 Mya. But logically, we know that's not the case --- it's not the "knowing" that happened 2.6 Mya, but rather the tool-making. The knowing is what the paleoanthropologists are doing right now.

That's why (A) is wrong and (C) is right.

Does all this make sense?

Mike
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Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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13 May 2015, 21:08
2
6
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
##### General Discussion
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Posts: 472
Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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04 Sep 2007, 01:33
1
2
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

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
[/u]

I would think the answer should be E. ??

C,

.........date at which something is known to .....is correct idiom
f.e: date at which the portrait is known to have been sold...

E is unidiomatic, completely.

we can say date of event {birth, death...test} f,e: we can say date of his {her, Ann`s} birth, but 'date of ' is not used directly with people or living things.
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Joined: 11 Jul 2009
Posts: 32
Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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18 Nov 2009, 19:58
2
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

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
[/u]

I would think the answer should be E. ??

B Had made suggested that it is not being done any more.Also it seems to refer to scientists
C correct --have dated and have made llel and earliest date at which - idiomatically correct
D to be making wrong tense and idiom
E humans who were known - changes meaning and also wrong tense
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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01 Dec 2009, 08:53
2
Dated at or Date at is correct idiom , so A,D, E are out

in B, "it" is ambiguous;
C looks better

hence C
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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28 Aug 2010, 23:16
2
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, 00:27
2
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

Subject is date => at which is correct. Either B or C
It is known that is unidiomatic.
Correct option C.
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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29 Aug 2010, 17:19
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 the fine-gr  [#permalink]

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28 Jan 2012, 11:13
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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06 May 2012, 13:51
Runner2 wrote:

I have the same question.
as per previous discussions, "have made" is || with "have dated". I think it is wrong because "have dated" referes to scientists and current time, but "have made" to people who lived thousand of years ago.

why is present perfect used?
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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07 May 2012, 18:36
1
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

[/u]

I would think the answer should be E. ??

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 : speaks about time not humans.
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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11 May 2012, 10:42
Code:
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 [u]when it is known that humans
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

OA:C
Background: Scientists have dated sediments. They found that the pieces of sharped-edged flakes were much older than samples previously found. This sentence structure has two parts that need to be parallel. The scientists have dated and the knowledge of the earliest date at which humans are to have made...

A: ...that humans made is not parallel to Scientists have dated INCORRECT
B: had made is also not parallel; so can be eliminated INCORRECT
C: at which humans are known to have made IS parallel to Scientists have dated CORRECT
D: to be making...not parallel INCORRECT
E: to make is not parallel because it is not in the PRESENT PERFECT tense INCORRECT

hope this helps guys....
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Re: Scientists have dated sharp-edged flakes of stone found in the fine-gr  [#permalink]

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11 May 2012, 10:56
Quote:
as per previous discussions, "have made" is || with "have dated". I think it is wrong because "have dated" referes to scientists and current time, but "have made" to people who lived thousand of years ago.

have made does not refer to to the people who lived thousands of years ago; however, it is modifying the earliest known date that is currently known (i.e the current theory, that these type of tools were only made 150,000 later)

Does this make sense?
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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04 Dec 2012, 05:29
1
I was not able to decide between A & C.

Can any1 explain the though process behind answering this question?

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,
Subject: Scientists
Verb: have dated

pushing back by more than 150,000 years the earliest date when it is
known that humans made stone tools.
Subject: the earliest date
Verb: is

Subject: humans
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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04 Dec 2012, 22:58
mikemcgarry wrote:
kuttingchai wrote:
I was not able to decide between A & C.
Can any1 explain the though process behind answering this question?

I'm happy to help with this.

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

The funny thing here is that (A) is more or less grammatically correct, but illogical. This is what is so tricky about GMAT SC --- it's not enough to be analyzing at the level of grammar. We have to take logic into account.

What the sentence is trying to say ----- (a) humans made tools 2.6 Mya, and (b) right now, we know this to be the case. There are two actions, happening at different times --- the tool making (2.6 Mya) and the knowing about the tool-making (right now).

Look at thhe grammatical structure in (A).
.... the earliest date when it is known that humans made stone tools.
What precisely is happening at that "when"-time? Is it the knowing or the making? Technically, the clause that immediately follows "when" is "it is known", so grammatically, this would suggest the knowing happened at this "when"-time, 2.6 Mya. But logically, we know that's not the case --- it's not the "knowing" that happened 2.6 Mya, but rather the tool-making. The knowing is what the paleoanthropologists are doing right now.

That's why (A) is wrong and (C) is right.

Does all this make sense?

Mike

Thank you Mike, that helped. I got that the "knowing" part is down right now.

Just one confusion

Do we have 2 independent clauses here?

Independent clause 1
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,

Independent clause 2
pushing back by more than 150,000 years the earliest date when it is known [that humans made stone tools.]
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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05 Dec 2012, 11:44
1
kuttingchai wrote:
Do we have 2 independent clauses here?

Independent clause 1
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,

Independent clause 2
pushing back by more than 150,000 years the earliest date when it is known (that humans made stone tools.)

Good question. No, there is only one independent clause, the first. A clause must have a bonafide subject and a bonafide verb --- this clause has the subject "scientists" and the verb "have dated."

The second, "pushing back by more than 150,000 years the earliest date ..." is a participial phrase. It has NO subject, and instead of a full verb (e.g. "pushes", "is pushing"), it just has a participle. See this blog: http://magoosh.com/gmat/2012/participle ... -the-gmat/.

What is a bit suspect about this sentence ---- ordinarily a participle would modify a noun, the noun it touches (the "Modifier Touch Rule"). Here, the participle modifies the action of the entire preceding phrase: this is a form that the GMAT SC tends to avoid. The question at the top is not attributed to a source. I would be suspicious of whatever source produced this question. There are so many bad sources of GMAT SC questions out there, and I think this may be from one of them.

Does all this make sense?

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

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06 Dec 2012, 22:41
mikemcgarry wrote:
kuttingchai wrote:
I was not able to decide between A & C.
Can any1 explain the though process behind answering this question?

I'm happy to help with this.

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

The funny thing here is that (A) is more or less grammatically correct, but illogical. This is what is so tricky about GMAT SC --- it's not enough to be analyzing at the level of grammar. We have to take logic into account.

What the sentence is trying to say ----- (a) humans made tools 2.6 Mya, and (b) right now, we know this to be the case. There are two actions, happening at different times --- the tool making (2.6 Mya) and the knowing about the tool-making (right now).

Look at thhe grammatical structure in (A).
.... the earliest date when it is known that humans made stone tools.
What precisely is happening at that "when"-time? Is it the knowing or the making? Technically, the clause that immediately follows "when" is "it is known", so grammatically, this would suggest the knowing happened at this "when"-time, 2.6 Mya. But logically, we know that's not the case --- it's not the "knowing" that happened 2.6 Mya, but rather the tool-making. The knowing is what the paleoanthropologists are doing right now.

That's why (A) is wrong and (C) is right.

Does all this make sense?

Mike

Thanks Mike for good explanation. I have chosen B, and think it is gramatically correct, but again here as you have explained "it is known" refers to the time when we find out about it but not humans first tool making time. Am i correct or i missed anything?
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Re: Scientists have dated sharp-edged flakes of stone found in  [#permalink]

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07 Dec 2012, 11:19
3
2
ziko 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

Thanks Mike for good explanation. I have chosen B, and think it is grammatically correct, but again here as you have explained "it is known" refers to the time when we find out about it but not humans first tool making time. Am i correct or i missed anything?

Dear Ziko,
First of all, yes, there's the logic issue --- the "earliest date" --- does this refer to the earliest date of knowing or the earliest day of making stone tools. Like (A), (B) also doesn't resolve this ambiguity.
Furthermore, (B) using something called the "empty it" ---- the "it" in "it is know that humans had made stone tools" is a pronoun that doesn't refer to any antecedent. It doesn't refer to anything. It is purely a grammatical placeholder, and in that sense it is "empty" --- unlike most bonafide pronouns, this "it" refers to nothing --- it has no valid antecedent. The GMAT generally avoids the "empty it" --- once or twice, I have seen an OA on official material involving an "empty it", but the GMAT uses the "empty it" far more frequently to construct wordy indirect phrases for incorrect answer choices.

Consider these two sentences:
(1) It is known that early humans used stone tools.
(2) Early humans are know to have used stone tools.
Both are grammatically correct, but the GMAT would consider the second one more direct, more powerful, and therefore a much better answer than the first.
Be suspicious of the "empty it" wherever you see it --- even if it's grammatically correct, it is in all likelihood not the correct answer.

Does all this make?

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

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09 Dec 2012, 00:32
mikemcgarry wrote:
ziko 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

Thanks Mike for good explanation. I have chosen B, and think it is grammatically correct, but again here as you have explained "it is known" refers to the time when we find out about it but not humans first tool making time. Am i correct or i missed anything?

Dear Ziko,
First of all, yes, there's the logic issue --- the "earliest date" --- does this refer to the earliest date of knowing or the earliest day of making stone tools. Like (A), (B) also doesn't resolve this ambiguity.
Furthermore, (B) using something called the "empty it" ---- the "it" in "it is know that humans had made stone tools" is a pronoun that doesn't refer to any antecedent. It doesn't refer to anything. It is purely a grammatical placeholder, and in that sense it is "empty" --- unlike most bonafide pronouns, this "it" refers to nothing --- it has no valid antecedent. The GMAT generally avoids the "empty it" --- once or twice, I have seen an OA on official material involving an "empty it", but the GMAT uses the "empty it" far more frequently to construct wordy indirect phrases for incorrect answer choices.

Consider these two sentences:
(1) It is known that early humans used stone tools.
(2) Early humans are know to have used stone tools.
Both are grammatically correct, but the GMAT would consider the second one more direct, more powerful, and therefore a much better answer than the first.
Be suspicious of the "empty it" wherever you see it --- even if it's grammatically correct, it is in all likelihood not the correct answer.

Does all this make?

Mike

Thanks Mike,
Your answer is very good. But does it mean that i alsways should avoid "emty it"? (of course whenever i am faced to two gramatically and logically correct answers).
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Re: Scientists have dated sharp-edged flakes of stone found in   [#permalink] 09 Dec 2012, 00:32

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