scientists have dated sharp-edged flakes of stone found in

[gmatkiller_24]

Hi, Ron.

can you tell me how to eliminate choice D and E, thank you!

[RonPurewal]

choice D is explained by this post:
https://www.manhattanprep.com/gmat/foru ... ml#p104759

[RonPurewal]

for choice E, what's your understanding?
here's a fun activity:
fill in this blank with something--anything--that makes sense:
May 1 is/was the date of _________.
(if that date has no significance to you whatsoever, feel free to change it--the specific date is not the point.)

depending on how you fill in that blank, you may already have all the tools you need to answer your own question.

[gmatkiller_24]

choice D is explained by this post:
https://www.manhattanprep.com/gmat/foru ... ml#p104759

got it，thanks！

[RonPurewal]

you're welcome.

[inc.manni]

Here the correct Ans uses Present Perfect "HAVE Made"

We need present perfect to refer to "Actions which happened at an indefinite (unknown) time before now"

Is my logic correct ???

[RonPurewal]

nope. that's not happening. in fact, that's not a tense at all (because 'to ___' is not a verb).

'to have ___ed' is the only 'EARLIER' form of 'to ___'.

since 'to ___' is not a verb, it doesn't have a tense of its own. rather, it is relative to the timeframe of the main sentence.
• 'to ____' = SAME timeframe as main sentence
• 'to have ____ed' = EARLIER than the main sentence

[RonPurewal]

e.g.,

The lawyer called hundreds of people known to use Company X's products.
--> the lawyer called people who used the products AT THAT TIME (when she made the calls).

The lawyer called hundreds of people known to have used Company X's products.
--> the lawyer called people who HAD used the products AT ANY TIME UP TO whenever she made the calls.

[RonPurewal]

note in particular that 'earlier' DOES NOT have to mean 'past'. rather, this depends entirely on the main sentence.
in particular, if the main sentence is in the future, then 'earlier' could also be in the future—as long as it's earlier than the main event.

e.g., let's say it's august right now.

In November, Company X will send out coupons to everyone known to have bought its products.
--> here, the 'buying' could occur at any time BEFORE the coupons are sent out in november.
in particular, this sentence includes people who buy things from company x in september or october, even though those are still future dates.

[KathyL227]

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


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,

Can I simply understand it as:

A when it is known that humans made (it means the exact date that is known to us)
B at which it is known that humans had made (same as A: it means the exact date that is known to us)
C at which humans are known to have made (Here means "humans could do sth…" are known to us )
D that humans are known to be making (that is not the correct word)
E of humans who were known to make (of is wrong)

In a nutshell, the construction in A and B means that the exact date was known to us...; in C, it means humans' activity is known since... (maybe humans actually started do... earlier than that data, but we just don't know yet.)

Not sure my understanding is correct.

Thanks.

Kathy

[RonPurewal]

the problem with A and B is that they refer (wrongly) to the time when we discovered this information—not to the time when humans made tools, as clearly intended in context.

[RonPurewal]

to see this, look at the verbs that follow 'when'/'at which':

A/
when it is known...
--> BAD
this is talking about when something became known. we SHOULD be talking about when people made tools!

B/
at which it is known...
--> BAD
this is talking about when something became known. we SHOULD be talking about when people made tools!

C/
at which humans are known to have made...
--> GOOD
THIS is what the sentence actually means!

[KathyL227]

to see this, look at the verbs that follow 'when'/'at which':

A/
when it is known...
--> BAD
this is talking about when something became known. we SHOULD be talking about when people made tools!

B/
at which it is known...
--> BAD
this is talking about when something became known. we SHOULD be talking about when people made tools!

C/
at which humans are known to have made...
--> GOOD
THIS is what the sentence actually means!

I get it.
Thanks.

[RonPurewal]

you're welcome.

[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

in A, "when it is known" must modify "date" and so this is not logic because the date is in the past but "it is known " is in present.
in B, "at which" can modify "it is known" or "human had made". both these modifications are not logic. the date is in the past, it can not be in present or past perfect
in C, "at which" can modify both " human are known" and " to have made" . but "at which" make sense only with " have known". logic. correct.
in D, "the date that" is ungrammatical. we need "at". this case is in spoken english.
in E, "the date of human" make no sense,