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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 [#permalink] New post 28 Aug 2010, 13:38
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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
B. at which it is known that humans had 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 [#permalink] New post 28 Aug 2010, 23:27
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

B. at which it is known that humans had 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] New post 04 Dec 2012, 04:29
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

that humans made stone tools
Subject: humans
Verb: made
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink] New post 04 Dec 2012, 10:59
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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
B. at which it is known that humans had 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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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink] New post 04 Dec 2012, 21:58
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
B. at which it is known that humans had 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] New post 05 Dec 2012, 10:44
Expert's post
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] New post 06 Dec 2012, 21:41
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
B. at which it is known that humans had 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] New post 07 Dec 2012, 10:19
Expert's post
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
B. at which it is known that humans had 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] New post 08 Dec 2012, 23:32
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
B. at which it is known that humans had 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] New post 09 Dec 2012, 14:10
Expert's post
ziko wrote:
Thanks Mike,
Your answer is very good. But does it mean that i always should avoid "empty it"? (of course whenever i am faced to two grammatically and logically correct answers).

Don't mechanically avoid the "empty it" --- nothing in grammar is completely mechanical. Most often, you will notice that the "empty it" phrasing is longer, wordier, less clear, less concise, less powerful. Most often, if two ways to say something are grammatically correct and one involves the "empty it", then then other will be more concise and more powerful. There are rare cases in which the most direct and efficient way to express something involves the "empty it." There are also GMAT SC problems in which four of the answers are incorrect, and the only possible correct answer involves an "empty it" --- remember, the answer to a GMAT SC question is going to be the best answer from among those five, not necessarily the very best way to express that idea. It will be grammatically correct, but not necessarily ideal.
Does all this make sense?
Mike :-)
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink] New post 03 Jan 2013, 17:37
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A. when it is known that humans made - when modifies "known", seems to suggest it was known 150,000 yrs ago
B. at which it is known that humans had made - same issue
C. at which humans are known to have made - correct answer
D. that humans are known to be making - known to be making is not crrect
E. of humans who were known to make - earliest date of humans doesnt make sense
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink] New post 24 Jan 2014, 20:56
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Re: Scientists have dated sharp-edged flakes of stone found in [#permalink] New post 24 Apr 2014, 04:37
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
B. at which it is known that humans had 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


Please underline the question.
Re: Scientists have dated sharp-edged flakes of stone found in   [#permalink] 24 Apr 2014, 04:37
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