天山-7-41

kevinlu21

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.

fatlara

以下是引用anyname在2005-3-23 13:41:00的发言：

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~~~

missdream

好象是跟题目相比,若选项中出现when引导的时间关系从句的强加或丢失都是错误的．

createdream

c

onglies

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.

xuedidage

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.  

GMAT阿驴

at which 优于　when 因为前者较明确

seastone

GWD 给出的答案为A

wjzm

此题XDF蓝皮书上有（section 10 Q14），所给答案是E，真是晕了

findjuhl

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

[此贴子已经被作者于2006-9-19 1:24:22编辑过]