特别是第一个解释完全体现了OG的宗旨。补充第二个解释 “ to have made tools ”应该是表明一种状态吧。Q41:
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 chose A, but the answer is C.
Why?
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 錯誤選項 畫線部分補充解釋date, when 為時間副詞不代特定名詞/ it 指涉不清
B. at which it is known that humans had made 錯誤選項 it 指涉不清/wordy/時態
C. at which humans are known to have made
D. that humans are known to be making 錯誤選項 to be making
E. of humans who were known to make 錯誤選項 脫節 句意怪異(推前那些做石器人類的最早日期)
I chose A, but the answer is C.
Why?
谁能解释一下吗？C为什么对啊？
现在语法区讨论的越来越少了。
我当时的理解是sbo be known to do sth是ets的fovor
虽然it is known that...通常有人们都认为...的意思,但是A的when和B的had made不OK吧.
agree.
thank you
A. when it is known that humans made 錯誤選項 畫線部分補充解釋date, when 為時間副詞不代特定名詞
B. at which it is known that humans had made wordy
C. at which humans are known to have made
D. that humans are known to be making 錯誤選項 to be making
E. of humans who were known to make of human错
Ｃ我也解释不清，但另外四个都有明确错误，只剩Ｃ了
A. when it is known that humans made 錯誤選項 畫線部分補充解釋date, when 為時間副詞不代特定名詞
swordhere不好意思，在具体题目中我能辨别怎么用，但解释不出来。刚刚在置顶贴“石林语法”中搜到了相关东东，希望能帮助你理解
2002/ time(具体时间) + when ；age in + which
同意楼上！ETS似乎更喜欢 BE KNOW TO DO/AS/FOR的形式，it is know that似乎比较少见
但是C中为什么要用have made呢?光是" at which humans are known to make" 多好呀???
up up up!!!
同問... 實在不明白為什麼要用完成式...
A雖然用when從語感上好像不是很精準, 但是我覺得沒錯啊...
本来选A，仔细考虑后改支持C。做题时看不惯at which，稍微查了一下，the date when....和the date at which都行。大家都同意答案在A和C间产生，简化后比较一下：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
C： (This finding) pushes back by X years the earliest date at which humans are known to have made tools.
1. A最大的问题是歧义。when... 本应作定语，但也是个完美的状语从句，意思就变成：当知道人类造工具这件事情的时候，this finding pushes back....。同一个东西可能作两种成分，并导致两个不同的意思，这种表达方式在GMAT中是禁止的。B 就没这个问题，因为at which...只能作定语从句，不能作状语。
2. be known to have done sth的问题。我觉得，当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。这里的情形显然属于后者。
所以选C
附known to do sth的例句：
1. 大全748：...few people are known to have recovered from the disease once the clinical symptoms have appeared.
2. 大全849：...few people have been known to taste it for the first time without requesting more.
3. og49：......satellites now known to orbit the distant planet.
A正确，when引导从句没有问题。C的时态不对，而且at which也指示，这个动作发生是在某个时间点上，这个情况是不可能用完成时态的。
如果C中把at which改成since which，还是正确的。
问一句关于选项D的，
1. that的使用方法对吗？
2. to be making怎么不对了？
我认为:
a中的when从句有修饰puting back 这个动作的嫌疑,
而用at which 只是修饰date,(这里我没有具体查,但我认为应该是对的) (突然感觉以前在哪个地方做过类似的题目,)
还有it is known that humans made tools
如前面所说,意思成了(大家都知道人们制作工具)扭曲了了作者的原意.
支持anyname, 特别是第一个解释完全体现了OG的宗旨。补充第二个解释 “ to have made tools ”应该是表明一种状态吧。
谢谢anyname, 同意此题选C，但对anyname的解释有不尽相同的看法，就A/B而言：
A. when it is known that humans made
B. at which it is known that humans had made
这里还有一个主要问题：A/B都没有指明when/at which是修饰从句中的it is known（知道“人类用石器”的时间）还是humans (had) made（人类用石器的时间）. 属修饰歧义错误。
本来选A，仔细考虑后改支持C。做题时看不惯at which，稍微查了一下，the date when....和the date at which都行。大家都同意答案在A和C间产生，简化后比较一下：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
C： (This finding) pushes back by X years the earliest date at which humans are known to have made tools.
1. A最大的问题是歧义。when... 本应作定语，但也是个完美的状语从句，意思就变成：当知道人类造工具这件事情的时候，this finding pushes back....。同一个东西可能作两种成分，并导致两个不同的意思，这种表达方式在GMAT中是禁止的。B 就没这个问题，因为at which...只能作定语从句，不能作状语。
2. be known to have done sth的问题。我觉得，当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。这里的情形显然属于后者。
所以选C
附known to do sth的例句：
1. 大全748：...few people are known to have recovered from the disease once the clinical symptoms have appeared.
2. 大全849：...few people have been known to taste it for the first time without requesting more.
3. og49：......satellites now known to orbit the distant planet.
太精彩了！鼓掌！
本来选A，仔细考虑后改支持C。做题时看不惯at which，稍微查了一下，the date when....和the date at which都行。大家都同意答案在A和C间产生，简化后比较一下：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
C： (This finding) pushes back by X years the earliest date at which humans are known to have made tools.
1. A最大的问题是歧义。when... 本应作定语，但也是个完美的状语从句，意思就变成：当知道人类造工具这件事情的时候，this finding pushes back....。同一个东西可能作两种成分，并导致两个不同的意思，这种表达方式在GMAT中是禁止的。B 就没这个问题，因为at which...只能作定语从句，不能作状语。
2. be known to have done sth的问题。我觉得，当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。这里的情形显然属于后者。
请注意：A选项中的push是用分词，不可以转成独立的句子：
pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools. 不可变成：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
因为如果when是状语从句的话，需要跟独立句子而不能跟分词。
请注意：A选项中的push是用分词，不可以转成独立的句子：
pushing back by more than 150,000 years the earliest date when it is known that humans made stone tools. 不可变成：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
因为如果when是状语从句的话，需要跟独立句子而不能跟分词。
"因为如果when是状语从句的话，需要跟独立句子而不能跟分词"? 不准确吧？看看OG159:
Five fledgling sea eagles left their nests in western Scotland this summer, bringing to 34 the number of wild birds successfully raised since transplants from Norway began in 1975.
raised也是分词。还有OG4：...to have it quickly processed into juice concentrate before warmer weather returns and rots the fruit. OG1 AB中的occurring when，没有说错在when...不能跟分词吧。
p.s.: 我上CD网速非常慢，不知为何？以前挺快的。。。
自己选的A，现在觉得C更好一些
大家的论述都很精彩
我想补充一下C选项的现在完成时的问题
用现在完成时是想表明在那一个时间点之前，都存在的情况。
也就是说
在XXXX年前，人们已经开始使用石器了
"因为如果when是状语从句的话，需要跟独立句子而不能跟分词"? 不准确吧？看看OG159:
Five fledgling sea eagles left their nests in western Scotland this summer, bringing to 34 the number of wild birds successfully raised since transplants from Norway began in 1975.
raised也是分词。还有OG4：...to have it quickly processed into juice concentrate before warmer weather returns and rots the fruit. OG1 AB中的occurring when，没有说错在when...不能跟分词吧。
p.s.: 我上CD网速非常慢，不知为何？以前挺快的。。。
确实，我还没有找到在ING后面一定不可以接从句的例子，在OG205中另有一例说明副词从句只能接有完整的句子而不能接介词结构：
205. The peaks of a mountain range, acting like rocks in a streambed, produce ripples in the air flowing over them; the resulting flow pattern, with crests and troughs that remain stationary although the air that forms them is moving rapidly, are known as "standing waves."
(A) crests and troughs that remain stationary although the air that forms them is moving rapidly, are
(B) crests and troughs that remain stationary although they are formed by rapidly moving air, are
(C) crests and troughs that remain stationary although the air that forms them is moving rapidly, is
(D) stationary crests and troughs although the air that forms them is moving rapidly, are
(E) stationary crests and troughs although they are formed by rapidly moving air, is
The main challenge in this sentence is to observe the agreement of subject and verb (the resulting flow pattern... is known...) despite the distraction of a complex intervening structure containing several plural elements (with crests and troughs...). Choices A, B, and D can, therefore, be eliminated because they use an incorrect plural verb form, are. Choice E uses the correct verb form, is, but it incorrectly introduces a dependent adverbial although clause into a prepositional phrase (with crests ...). Choice D also makes this error. Such dependent clauses can only occur in the predicates of full clauses. C, the best choice, uses the correct verb form, is, and correctly puts the although clause inside the predicate of the relative clause (that... rapidly).
E为什么不对？大家怎么上来就把E排除了？
ABCD都有个共同的严重问题，就是歧异,这犯了ETS的大忌。我们不知道到底是“人类制造石器工具”的时间被推前了还是“知道人类制造石器工具”的时间被推前了。这个歧异产生的根源是know作为从句谓语，使得date看起来好像指得是“know”发生的时间。
而E彻底解决了这个问题。是“已知制造石器工具的人存在的最早时间”被推前了。
Actually, date at which is better.
Humans who were known to make... 当时就知道人类...
humans who are known to make... 现在知道那时的人类.
本来选A，仔细考虑后改支持C。做题时看不惯at which，稍微查了一下，the date when....和the date at which都行。大家都同意答案在A和C间产生，简化后比较一下：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
C： (This finding) pushes back by X years the earliest date at which humans are known to have made tools.
1. A最大的问题是歧义。when... 本应作定语，但也是个完美的状语从句，意思就变成：当知道人类造工具这件事情的时候，this finding pushes back....。同一个东西可能作两种成分，并导致两个不同的意思，这种表达方式在GMAT中是禁止的。B 就没这个问题，因为at which...只能作定语从句，不能作状语。
2. be known to have done sth的问题。我觉得，当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。这里的情形显然属于后者。
所以选C
附known to do sth的例句：
1. 大全748：...few people are known to have recovered from the disease once the clinical symptoms have appeared.
2. 大全849：...few people have been known to taste it for the first time without requesting more.
3. og49：......satellites now known to orbit the distant planet.
有道理~
现在又充分的理由排除A了~
VOTE FOR C~~~
状语从句， or adverbial clause, or more generally adverbial modifier, is used to modify a action(verb) whether the action is presented in its participial form or indefinitive form.
and thus logically it can not be used to modify a prepersitional phrase.
pushing back by more than 150,000 years the earliest date when it is known that humans
made stone tools.
Just by reading this, it is logically wrong. It seem like the time at which we know this fact(humans made tools) is pushed back 150,000 years. This is clearly not what the sentence intended.
此题XDF蓝皮书上有（section 10 Q14），所给答案是E，真是晕了
找到原文，不过似乎对选答案没太大帮助
More than 2,600 sharp-edged flakes, flake fragments, and cores (cobbles from which flakes have been removed), found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia, have been dated to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the known date at which humans were making stone tools.
http://www.archaeology.org/9703/newsbriefs/tools.html
"be known to do sth." and "at which date" are the reasons why C is the correct answer.
用完成式是因为作者想强调,人类在这个时间就已经开始制作工具了,因为不排除还有未发现的证据能将这一日期再次提前.在本句中,强调的是在此时点,就已完成该动作.
选项A和C在语法上都正确,但只有C精确的表达了科学家想表达的意思.
用完成式是因为作者想强调,人类在这个时间就已经开始制作工具了,因为不排除还有未发现的证据能将这一日期再次提前.在本句中,强调的是在此时点,就已完成该动作.
选项A和C在语法上都正确,但只有C精确的表达了科学家想表达的意思.
用完成式是因为作者想强调,人类在这个时间就已经开始制作工具了,因为不排除还有未发现的证据能将这一日期再次提前.在本句中,强调的是在此时点,就已完成该动作.
选项A和C在语法上都正确,但只有C精确的表达了科学家想表达的意思.
Exactly. That's the point we learned in the high school.
We seem to have forget them because of the long time. U c, seem to have done
对于A的解释用定从和状从来排除有点一竿子打死一船人的情况
如果如大家所说那对于when引导的定语从句是不是都会有状语从句的歧义呢？
这样说了when在GMAT里的使用那真是如履薄冰了
个人理解：
A when本身没有错，可能只是错在it is know that 这个ETS不喜欢的结构，因为it的指代歧义存在。
C ETS更加喜欢，know to这样的结构
但是对于C里的have done后接明显的过去时标志，这样的使用确有不妥之处
anyway，C 里的at which 即使换成when 也依然是答案
大家只有记住，看到 it is know that和know to并存的时候长个心眼了
牛牛们，别笑话我，我到现在还不知道为什么不选E。请详细解释一下。脑子秀逗了。我看这题想的时间最长，然后把后面的pace也弄乱了，结果这一套模得极差
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.
这题我也不明白啊,XDF给的答案是E, E的of用的是不太好,不明白这是什么结构,不过C其实问题也很多啊,前面的NN们讨论出用完成时是对的(总觉得有点牵强......),但那个 are又怎么解释呢
答案是比出来的,那我觉得E应该比C好
呼唤大家再讨论讨论
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.
这题我也不明白啊,XDF给的答案是E, E的of用的是不太好,不明白这是什么结构,不过C其实问题也很多啊,前面的NN们讨论出用完成时是对的(总觉得有点牵强......),但那个 are又怎么解释呢
答案是比出来的,那我觉得E应该比C好
呼唤大家再讨论讨论
我就是根据were排除E的
首先问个问题，你觉得humans被谁known？应该是被scientists吧？那既然scientists都have dated了，这里是不是应该are known呢？
找到原句了http://www.answerbag.com/q_view/279672
不过不太一样
..., pushing back by more than 150,000 years the known date at which humans were making stone tools.
原句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,用的是现在完成时,根据一个句子不能同时有过去时和现在时 排除abe
还有大断的时间 和 从现在起往前推的时间都用现在完成时
来源于XDF
模考的时候选C,REVIEW的时候觉得E才是正确答案:
1.A,B,C,D都是定语从句修饰date,when和at which都可以引导,at which清晰一点.D的that肯定不对.
2.ABC都有歧义,不管是when还是at which,(A,B)放在定语从句中都做一个时间状语的作用,代替earliest date,在A,B中,这个时间状语就近修饰it is known....即知道(原始人制造石器)的时间.这个时间状语实际上应该修饰humans made stone tools,而不是it is known.即the earliest (known) date when humans made stone tools
C一样有歧义,at which修饰humas are known,而不是不定式to have made
E虽然第一眼看上去不爽,但是却找不出毛病来,the earliest date of humans (who were know to make ...),(已知的制造石器的)人 的最早的时间.
这个date of 还不能省,虽然earliest humans更精炼,因为前面的pushing back by more than 150,000 years.
至于E答案的were known,看起来有点怪,但实际上符合逻辑,从earliest date以后,讲的都是过去对原始人造石器的认识,正是新的发现把旧的认识时间给提早了150,000年.
其实原句是最清晰的,出题者出题时把修饰关系给严重扭曲了:
More than 2,600 sharp-edged flakes, flake fragments, and cores (cobbles from which flakes have been removed), found in the fine-grained sediments of a dry riverbed in the Afar region of Ethiopia, have been dated to between 2.52 and 2.60 million years ago, pushing back by more than 150,000 years the known date at which humans were making stone tools.
原句: known date 清晰没话说,地道英语
at which humas were..... at which做时间状语修饰humans were making,清晰
date that humans are known to be making
date 后面可以跟that???
谢谢anyname, 同意此题选C，但对anyname的解释有不尽相同的看法，就A/B而言：
A. when it is known that humans made
B. at which it is known that humans had made
这里还有一个主要问题：A/B都没有指明when/at which是修饰从句中的it is known（知道“人类用石器”的时间）还是humans (had) made（人类用石器的时间）. 属修饰歧义错误。
本来选A，仔细考虑后改支持C。做题时看不惯at which，稍微查了一下，the date when....和the date at which都行。大家都同意答案在A和C间产生，简化后比较一下：
A：(This finding) pushes back by X years the earliest date when it is known that humans made tools
C： (This finding) pushes back by X years the earliest date at which humans are known to have made tools.
1. A最大的问题是歧义。when... 本应作定语，但也是个完美的状语从句，意思就变成：当知道人类造工具这件事情的时候，this finding pushes back....。同一个东西可能作两种成分，并导致两个不同的意思，这种表达方式在GMAT中是禁止的。B 就没这个问题，因为at which...只能作定语从句，不能作状语。
2. be known to have done sth的问题。我觉得，当be known 和 do sth的发生的时间一致时，用be known to do sth；而do sth发生在be known之前时，则要用be known to have done sth。这里的情形显然属于后者。
所以选C
附known to do sth的例句：
1. 大全748：...few people are known to have recovered from the disease once the clinical symptoms have appeared.
2. 大全849：...few people have been known to taste it for the first time without requesting more.
3. og49：......satellites now known to orbit the distant planet.
请问蓝色部分的字体:
这部分说得有道理.做题时候我也想到,但是我的问题是,您说的这个情况,是不是也同样适用于C呢?
C: at which humans are known to have made
at which 修饰"humans被知道(用石器)"的时间 (are known to have made),而不是修饰人类"用石器"的时间.
简而言之,C中的 at which为啥就不能修饰 are known这个动词了? at which 为啥就一定要修饰 to have made 这动词了呢??
这点上我认为ABC没有区别啊?谁能说说?
我觉得有时候并正确选项并不一定毫无瑕疵，只是它相比其它选项来说是最优选择。
这也是ETS惯用伎俩中的一招。
对于A的解释用定从和状从来排除有点一竿子打死一船人的情况
如果如大家所说那对于when引导的定语从句是不是都会有状语从句的歧义呢？
这样说了when在GMAT里的使用那真是如履薄冰了
个人理解：
A when本身没有错，可能只是错在it is know that 这个ETS不喜欢的结构，因为it的指代歧义存在。
C ETS更加喜欢，know to这样的结构
但是对于C里的have done后接明显的过去时标志，这样的使用确有不妥之处
anyway，C 里的at which 即使换成when 也依然是答案
大家只有记住，看到 it is know that和know to并存的时候长个心眼了
之前众说纷纭的觉得有点乱，这个非常清楚！！
请问蓝色部分的字体:
这部分说得有道理.做题时候我也想到,但是我的问题是,您说的这个情况,是不是也同样适用于C呢?
C: at which humans are known to have made
at which 修饰"humans被知道(用石器)"的时间 (are known to have made),而不是修饰人类"用石器"的时间.
简而言之,C中的 at which为啥就不能修饰 are known这个动词了? at which 为啥就一定要修饰 to have made 这动词了呢??
这点上我认为ABC没有区别啊?谁能说说?
还是不明白A里面the date when it is known that humans made stone tools.里面，when会不会被认为修饰it is known？而不是修饰made?
以及C里面 the earliest date at which humans are known to have made stone tools.这个at which会不会被认为修饰are known而不是修饰have made stone tools？
umm...有点眉目了，或许是因为有is和are的存在，所以at which/when只会修饰后者，否则的is和are应该换成was和were。所以是不会引起歧义修饰的。而A的错误应该仅在于1、when不如”“介词+which”“ 2、be known to do在描述一件早已存在却现在才发现的事情时，才是更简洁地道的表达方法。
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.
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.
同学，2.6 million应该= 2，600，000吧？
换句话说，2,600,000-2,520,000=80,000
而且我觉得150,000不是和 (2,600,000-2,520,000)之差比较。应该是本来有个时间，但这个时间比2.52mil-2.6mil年前晚
anyname 发表于 2005-3-23 13:41
本来选A，仔细考虑后改支持C。做题时看不惯at which，稍微查了一下，the date when....和the date at which ...
zuozuox 发表于 2009-8-1 19:12
但是C的完成时态真的是个问题，为什么用完成是呢？
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