Q34:

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.

1. when it is known that humans made 
2. at which it is known that humans had made
3. at which humans are known to have made
4. that humans are known to be making
5. of humans who were known to make

My intuitive answer is C, while A makes sense to me too.

I prefer A

C：at介词有问题，2.现在完成时有问题

从GMAT出题的TRICK风格来讲，A更像GMAC的乏走狗。前面用个现在完成时，后面也弄个同样的东东，但其实后面提到的事是过去发生的并没有延续到现在，还是应该用过去式。有梦友找到原文出处，原文用的是过去进行时，were，这应该也算是过去式范畴的一个佐证吧。就A吧。

只能是 A，B 和 C的which 前加了 at，不对。

D 的 to be making  不对。

E 修饰重点不对，这里修饰的是 date，而不是human

...date at which ... here the use of at makes perfect sense.

I'd choose C over A for conciseness in meaning and fluency in construction.

Open for discussion!

不好意思,能不能劳驾NN再给看一看,刚才在逻辑题干中找到一个和这个语法题中时间表述相同的表达,如果这个用法成立,那么是不是说明C的致命弱点就是时态了呢?

GWD-9-Q40:

Agricultural societies cannot exist without staple crops. Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods. All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams. Therefore, discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there.

本题:

....more than 150,000 years the earliest date....

C    at which humans are known to have made

强烈推荐c

a中when修饰的时间有歧义，可能是it is known的时间

The tense in C is alright.

 ....arisen at there.

date when...  is correct.   

A is the best.

Do you know the date when the house was built?  ------> this is a correct sentence.

[此贴子已经被作者于2006-8-25 12:46:45编辑过]