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Scientists have dated sharp-edged flakes of stone found in

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VP
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Joined: 07 Nov 2005
Posts: 1118
Location: India
Scientists have dated sharp-edged flakes of stone found in [#permalink]

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New post 25 Apr 2006, 05:07
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A
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C
D
E

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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

Give Explaination plz.
Director
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Joined: 24 Oct 2005
Posts: 659
Location: London
 [#permalink]

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New post 25 Apr 2006, 05:38
Tough one.

A. when it is known that humans made - date when incorrect
B. at which it is known that humans had made - known that humans had made doesnt seem right.
D. that humans are known to be making - implies that humans are making date.
E. of humans who were known to make - date of humans??

Between B and C, I am going with C
SVP
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Joined: 24 Sep 2005
Posts: 1885
Re: SC :Flakes [#permalink]

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New post 25 Apr 2006, 06:07
buzzgaurav 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

Give Explaination plz.


The usage of "it" in A and B is ambiguous ...although we know that "it" points to an implicit subject, "it" can be understood to modify "the earliest date" --> cross A and B

C looks fine: we need to use present perfect " have made" to indicate something happened in past.

D: the action of "make" no longer takes place --> "to be making" is incorrect!

E: "humans" is a broad and general noun --> the use of "who ..." to modify "humans" is unsuitable

Go for C.
Manager
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Joined: 13 Dec 2005
Posts: 224
Location: Milwaukee,WI
 [#permalink]

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New post 25 Apr 2006, 06:30
extremly good one ... Got C

A. when it is known that humans made --- it is ambigious
B. at which it is known that humans had made ---it is ambigious
C. at which humans are known to have made ---- correct
D. that humans are known to be making --humans were making dates
E. of humans who were known to make ----dates of human . ..
  [#permalink] 25 Apr 2006, 06:30
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Scientists have dated sharp-edged flakes of stone found in

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