Prep-SC-1-45 时态。

The application of a new method for analyzing the chemistry of tooth enamel allows scientists to

examine molars of prehuman ancestors and determining that their diets were more varied than had

been supposed.

(A) The application of a new method for analyzing the chemistry of tooth enamel allows scientists to

examine molars of prehuman ancestors and determining

(B) Through the application of a new method for analyzing the chemistry of tooth enamel, the

molars of prehuman ancestors were examined by scientists who determined

(C) When they applied a new method for analyzing the chemistry of tooth enamel, scientists

examined molars of prehuman ancestors, determining

(D) Applying a new method for analyzing the chemistry of tooth enamel, the molars of prehuman

ancestors have been examined by scientists, who determined

(E) Applying a new method for analyzing the chemistry of tooth enamel, scientists have examined

molars of prehuman ancestors and determined

Key:E

本题我纠结于C和E之间。我知道C莫名奇妙的加出一个when引导的时间状语从句不好。

但是红字部分的时态我是在看不懂。我有两个问题。

”that their diets were more varied than had been supposed"

1. 红字部分是一个 科学结论或实验结果 为什么不用 their diets are而用一般过去时were。

    就算把 实验 结果 看成是一个一般事件，那么 究竟是 原始人 的 食物很丰富 在前， 还是 suppose的内容在前。

    为什么不是 that their diets had been more varied than was supposed

    而是 that their diets were more varied than had been supposed

2. E的主句的时态如何确定的？有什么依据。

    have determined that 为什么引导(were)一般过去时的从句。

    对gmat里的时态混用，总是不明白。

向大家求教。  

这不是科学事实，而只是陈述一个研究结果，客观真理，客观存在，科学事实应该是这样的：
The earth moves around the sun.
Shanghai lies in the east of China.
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因为并不是说明一个事实，所以were的时态是根据determine来的.
that their diets were more varied than (they) had been supposed.
suppose确实发生在their diets were more varied这件事情被determine的前面，自然就要用过去完成时.(换句话说suppose发生在determine前面)。
--
关于have examined，从语法上讲用examined也没错，只是完成时"更加强调结果"。
终结性情景分为四种：
前两种针对持续性动作：processes(过程),accomplishments(完成)
后两种针对瞬时动作(可以用现在完成时也可以用一般过去时)：  transitional events(转态事件),transitional acts(转态行为). ---关键在于“转态”。
举个状态例子：She opened the door,说明了门最终处于开启状态，与最初状态不同。这里也可以用完成时：She has opened the door.
这里的examine就是属于一个transitional act.所以是可以用现在完成时的.

同样的determine也用了现在完成时，但是后面的陈述始终是发生在过去的，所以用了一般过去时。

谢谢版主解答，那我就继续问了。
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“这不是科学事实，而只是陈述一个研究结果，客观真理，客观存在，科学事实应该是这样的：
The earth moves around the sun.
Shanghai lies in the east of China.”
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我想了想，希望版主指正。

所谓：客观的事实和科学事实 用SIMPLE PRESENT，是有条件的。

这个条件是: 这个事实 必须是 从过去-到现在-到将来一致发生着，或者存在的。

如果，这个事实只是过去的事实，现在不发生，将来也不发生。就只能用SIMPLE PAST时。（不管是不是事实，不管是不是科学发现）

比如 that their diets were more varied
        改成 that their diets is more varied
        

前一句的意思是：过去曾经有原始人，他们的食物很丰富。 而现在，将来都没有原始人了。（这个事实只是过去的事实）

后一句的意思就是说：现在还存在原始人， 这些原始人的食物还是很丰富的，并且 将来 还有原始人，他们的食物还是很丰富。（也就是说这个事实永远存在）

后一种理解不和逻辑，所以不能使用 SIMPLE PRESENT。

不是的，要跟前面的determine连起来看，就跟这个句子一样：Experts have determined that the signature was forged.
用过去时不是说那个事实是过去的事实，而只是为了时态一致。
that their diets is more varied 也并没有表达过去、现在、将来还有原始人的意思

"Experts have determined that the signature was forged."
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这里的主句Experts have determined的谓语部分的aspect是完成体（perfective)；但是主句的tense怎么都是现在时(present)吧。而从句 the signature was forged的tense是past，主句和宾语从句的tense是不一致的：版主为什么说：是一致的？ 我认为，主从句时态不一致是可以啊。

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另外 回到我说的 题目里

这里 有三个 事件

Scientist determine     than is expected   their diets were more varied

      A                                      B                                     C

按照道理 ，时间顺序应该是：  C在最前------B在之中-------A在最后

为什么 B在A之前要用 past perfective 而C在 B和A之前，却不用past perfective。

时态的一致是逻辑上的一致而不是语法上的一致，不是前面过去时后面也过去时，而是主句发生的事情在过去，那么从句的时态是要建立在那个“过去”的基础上的.

第二个问题我在2楼有说到：suppose确实发生在their diets were more varied这件事情被determine的前面，自然就要用过去完成时.(换句话说suppose发生在determine前面)。
suppose不是跟their diets were more varied比，而是跟have determined比。

(E) Applying a new method for analyzing the chemistry of tooth enamel, scientists have examined

molars of prehuman ancestors and determined that their diets were more varied than had

been supposed.

我觉得 
                                that their diets were more varied than had been supposed.这句话，你必须要在主句的大环境下理解，“their diets were more varied”是determine的内容，换句话说，在determine之前，他们还没有发现their diets were more varied，那么发现的内容相比之前估计的内容suppose来说，肯定是以前先估计了，后来才发现不是像估计的那样，所以supposed最靠前，应该用过去完成时

been supposed.

我觉得 
                    that their diets were more varied than had been supposed.这句话，你必须要在主句的大环境下理解，“their diets were more varied”是determine的内容，换句话说，在determine之前，他们还没有发现their diets were more varied，那么发现的内容相比之前估计的内容suppose来说，肯定是以前先估计了，后来才发现不是像估计的那样，所以supposed最靠前，应该用过去完成时