scientists have dated sharp-edged flakes of stone found in

[kkunal]

i think the real problem with the construction in choice (a) is that the clause following "when" is "it is known". in other words, that choice suggests that the fact is (was?) known at that date, an interpretation that clearly doesn't make sense in context.
in the correct answer, the "at which" is followed by a clause whose subject is "humans", and which describes the actual action that took place at that date. therefore, i think the idea is that this clause more accurately describes the chronology of the events: i.e., the toolmaking happened at that date, and the fact is known now.

I agree and this is how I eliminated choice A.
But isn't there another issue, which I have seen in quite a few official questions, with the usage of [i]made[/] as well? It implies that human beings no longer make stone tools now, which is obviously incorrect.

[jnelson0612]

i think the real problem with the construction in choice (a) is that the clause following "when" is "it is known". in other words, that choice suggests that the fact is (was?) known at that date, an interpretation that clearly doesn't make sense in context.
in the correct answer, the "at which" is followed by a clause whose subject is "humans", and which describes the actual action that took place at that date. therefore, i think the idea is that this clause more accurately describes the chronology of the events: i.e., the toolmaking happened at that date, and the fact is known now.

I agree and this is how I eliminated choice A.
But isn't there another issue, which I have seen in quite a few official questions, with the usage of [i]made[/] as well? It implies that human beings no longer make stone tools now, which is obviously incorrect.

That is an interesting point. I think that the other meaning problem already discussed is a bigger issue. That said, it is interesting to note that the correct answer contains "have made", indicating that the tool making happened in the past and continues today, rather than just the simple past tense "made".

[Suapplle]

this is one of those problems from which you can learn about the ways in which these sorts of constructions are used. indeed, it is precisely from these sorts of problems that you must learn about the niceties of these constructions, as the gmat's usage can, and does, sometimes vary from that of other sources.

in this sort of construction, i'm pretty sure that either "when" or "at which" would be acceptable. (clearly, the latter is acceptable -- it appears in the correct answer, after all -- but i wouldn't object to the former.)
if you want to get really subtle, i think (not 100% sure) that "the date when" is used for actual, precise calendar dates, whereas "the date at which" is used for the usually more vague dates of historical events, such as the one in this problem. but i'm sure the test is not going to depend on this sort of nuanced difference.

i think the real problem with the construction in choice (a) is that the clause following "when" is "it is known". in other words, that choice suggests that the fact is (was?) known at that date, an interpretation that clearly doesn't make sense in context.
in the correct answer, the "at which" is followed by a clause whose subject is "humans", and which describes the actual action that took place at that date. therefore, i think the idea is that this clause more accurately describes the chronology of the events: i.e., the toolmaking happened at that date, and the fact is known now.

as for your other question, this isn't really a perfect tense, because it's actually not a tense at all -- it's an infinitive.
probably the easiest way to go here is to remember this as an idiomatic usage of the construction "known to". if the action is in the present, then you use "known to VERB"; if the action is in the past, then you use "known to have VERBed". as far as i know, these are the only two possible forms.

Hi,Ron,in this sentence,
the earliest date when it is known that Humans made stone tools.
We can rewrite it :
#1
It is known that humans made stone tools at the earliest date.
Or
#2
It is known that humans made stone tools at the earliest date.
"When" modify the main sentence or subordinate sentence?thanks!

[RonPurewal]

the earliest date when it is known that Humans made stone tools.
We can rewrite it :
#1
It is known that humans made stone tools at the earliest date.
Or
#2
It is known that humans made stone tools at the earliest date.
"When" modify the main sentence or subordinate sentence?thanks!

#1 is nonsense. ("It is known" can't apply to past dates.) So it's #2.

If you wanted to write something like #1, you'd put the modifier next to what it's actually supposed to modify.
For instance, the meaning of I read that taxes are going to increase in today's newspaper is clear enough, but there's no reason to put "in today's newspaper" so far away. You'd want to write I read in today's newspaper that taxes are going to increase.

[lindaliu9273]

Hi instructors,

In A/B, does "it" refer to "that humans made stone tools"?
I'm a little confused because I can't find antecedent of "it". But this usage sounds good.

Thanks a lot!

[RonPurewal]

Read here:
post49622.html#p49622

[AbhilashM94]

Ron - question on tense.
Not sure if GMAT tests such subtle issues in tense.

at which humans are known to had made
OR
at which humans are known to have made

[tim]

I'm assuming your question is whether either of your examples contain errors. I can't think of an example where "known to had made" would ever be correct. If this was not your question, but your question was instead whether the GMAT would test this, I see no reason why not.

[thanghnvn]

Hi, all

Please can anybody help me with this sentence correction 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, 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 ans is c but I chose a. Why a is incorrect？Shouldn't "date" be followed with "when"? And is it necessary to use past perfect tense as in choice c? I would like to choose the simple past tense.

Thank you in advance for your kind help~

babayu

this is wonderful problem.

consider the problem from two points of view.

1, regarding idiom.

it is simple and clear that there pattern ,d and e is not idiomatic. we have only one idiom

human are known to have done.

2. regarding adverb of time

"at which" in choice B CORRECTLY refer to "had made" grammatically. but what is wrong is past perfect, which refer to a specific time in the past.

regarding A

the pattern in A make "when" refer to "it is known" . "when " in A can not refer to "human made". and because "when" refer to "it is known", is is not logic.

is my thinking correct? if you find my explanation good, pls , say thank you to encourange me

[thanghnvn]

Hi, all

Please can anybody help me with this sentence correction 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, 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 ans is c but I chose a. Why a is incorrect？Shouldn't "date" be followed with "when"? And is it necessary to use past perfect tense as in choice c? I would like to choose the simple past tense.

Thank you in advance for your kind help~

babayu

"at which" in B is right because

we can write

it is known that humans made stone tool AT that date

"when" in A is wrong because we can not write

it is known that human made stone tool when

"WHEN' must refer to "it is known" and so is wrong logically.

[jlucero]

Hi, all

Please can anybody help me with this sentence correction 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, 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 ans is c but I chose a. Why a is incorrect？Shouldn't "date" be followed with "when"? And is it necessary to use past perfect tense as in choice c? I would like to choose the simple past tense.

Thank you in advance for your kind help~

babayu

"at which" in B is right because

we can write

it is known that humans made stone tool AT that date

"when" in A is wrong because we can not write

it is known that human made stone tool when

"WHEN' must refer to "it is known" and so is wrong logically.

I don't see a question here, so I'm assuming you're good.

[eggpain24]

Hi，ron

can you shed more light on choice D?

is it wrong for the use of "that" and "known to be making"

I cannot fully articulate the mistake here.

Thank you~

[thanghnvn]

[quote="yu.baba2008"]Hi, all

Please can anybody help me with this sentence correction 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, 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

pls, look at choice B
grammatically , "at which" refers to "is known" or "had made".? pls, tell me

of course, I know that "is known" a present time and "had make" a past perfect can not go with a point of time in the past. but , I still want to know "at which" refer to which verb grammatically

[RonPurewal]

from the correct answer, it's clear that context matters and that you need to use common sense to answer that question.

in the correct answer, "the date at which..." is most certainly talking about "...to have made stone tools" (since "is known" refers to current knowledge).

on the other hand, one could write a similar sentence in which the other verb is the reference.
e.g.,
... the earliest date at which it was known that blood circulates through the human body
in this sentence, which is also correct, the date refers to "it was known".

[RonPurewal]

... so you're correct in eliminating that choice on the basis of "had made".