新PREP1-256，求助

jackcxp

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 原句的earliest最高级修饰date强调时间点，所以使用at which由于when；A，B选项逻辑意思严重违背原句意思，A，B选项的意思是humans made stone tools被it is known的时间被push back...；原句是想说human are known to have made stone tools的时间被pushing back；过去已经发生的事情，现在被发现也是现在完成时使用的情况之一。

原句的earliest最高级修饰date强调时间点，所以使用at which由于when；A，B选项逻辑意思严重违背原句意思，A，B选项的意思是humans made stone tools被it is known的时间被push back...；原句是想说human are known to have made stone tools的时间被pushing back；

过去已经发生的事情，现在被发现也是现在完成时使用的情况之一。

-- by 会员 Liu_leaf (2009/7/15 23:25:00)

严重同意，when和at which并不是最大的问题，A最大的错是错在扭曲本来想表达的句意。

subaru6385

嗯 明白了 感谢！

sheilaring

主要的问题 是在于从句后的主语 按照逻辑 前面讲的 是指人类 所以后面从句的主语应该是humans  
when ,at which are all okay here.

rebekah705

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

我觉得A主要问题在 定语从句引导词用了When而没用which, 这里要修饰的先行词是date, 而若用when 引导，前面不能是date。 还原来开，it is known that humans made stone tools when, 后面这句可以看成it 是形式主语，再把date 带入从句， 则句子成为that humans made stone tools is known date 这里缺少一个介词。

B 虽然解决了when的问题，可是语义不对。同理调换顺序后等于 that humans had made stone tools is known at date.  这样来看，date指的是人类最早开始做石器这件事 被知道 的时间， 而非指所知道的 人类最早开始做石器的 时间。 体会。

C 人类被知道开始做石器的时间。 date 指 have made stone tools.   这里的 不定时用to have done, 表示动作的已经完成，完全可以。

vampireking

可以看一下国外论坛上的解释

Hi, all

Please can anybody help me with this sentence correction question:

Scientistshave dated sharp-edged flakes of stone found in the fine-grainedsediments of a dry riverbed in the Afar region of Ethiopia to between2.52 and 2.60 million years ago, pushing back by more than 150,000years 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

Theans is c but I chose a. Why a is incorrect？Shouldn't "date" be followedwith "when"? And is it necessary to use past perfect tense as in choicec? I would like to choose the simple past tense.

Thank you in advance for your kind help~

babayu


thisis one of those problems from which you can learn about the ways inwhich these sorts of constructions are used. indeed, it is preciselyfrom 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.

inthis sort of construction, i'm pretty sure that either "when" or "atwhich" would be acceptable. (clearly, the latter is acceptable -- itappears in the correct answer, after all -- but i wouldn't object tothe 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 ofhistorical events, such as the one in this problem. but i'm sure thetest is not going to depend on this sort of nuanced difference.

ithink the real problem with the construction in choice (a) is that theclause following "when" is "it is known". in other words, that choicesuggests that the fact is (was?) known at that date, an interpretation that clearly doesn't make sense in context.
inthe correct answer, the "at which" is followed by a clause whosesubject is "humans", and which describes the actual action that tookplace at that date. therefore, i think the idea is that this clausemore accurately describes the chronology of the events: i.e., thetoolmaking 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.
probablythe easiest way to go here is to remember this as an idiomatic usage ofthe construction "known to". if the action is in the present, then youuse "known to VERB"; if the action is in the past, then you use "knownto have VERBed". as far as i know, these are the only two possibleforms.

dumengxuan

12套 挨千刀的居然对错一套题答案当时就想死了

AnnieFFish

Liu_leaf 发表于 2009-7-15 23:25
Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry river ...

醍醐灌顶！
确实AB这个意思被扭曲
看来还是要好好理解句意

考拉飞起

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.

daisylol

Liu_leaf 发表于 2009-7-15 23:25
Scientists have dated sharp-edged flakes of stone found in the fine-grained sediments of a dry river ...

同意！               

idsamsang

个人觉得这道题目的关键在于 知道动作和时间之间的逻辑。 A 和 B 都是说人类制作工具这件事在150000年就被知道，显示不符合逻辑。作者要表达的是在150000年人类就已经制作工具了。那么只有 C 可以准确的说明 人类150000年也就是最早的这个时间知道去制作工具。