GWD17-Q38:

gmatwc

关于is thought to have lived about 140000 years ago, 我有一点想法

如果反着想，有140000years ago 要用过去时的话，怎么改原句，难道改成 is thought to lived about 140000years ago?

所以有可能在 is thought 这种被动情况下，又要表达是过去的事情，加上这个have

纯属琢磨，希望后人给明确解释

红尘道士

http://forum.chasedream.com/GMAT_SC/thread-91380-1-1.html
这个帖子讲的很清楚

红尘道士

is thought to have lived about 140000 years ago
表示是别人的看法，不是作者的看法

BeBrave2011

以前没有见过B这种用法，在网上搜到一个解释，支持了你的观点。

The aspect of infinitives
Although in all of the followingsentences we use go, each sentence refers to a different time:
You had to go home.(past time)
Does she go home every night? (present time)
I will never go home. (future time)
So it is not go that marksthe time of the sentence but had, does and will. Somethingsimilar happens when reporting with the help of passive voice:
My grandfather is known to like red wine. (= People knowthat my grandfather likes red wine.)
Is known marks present time, and to like refers to the sametime. If we put the verb in the main clause into the past tense, to like will refer to past time,too:
My grandfather was known to like red wine. (= People knewthat my grandfather liked red wine.)
We can see that the infinitives goand like in the examples above do not, in themselves, express eitherpast, present or future time, but they refer to the same time as expressed bysomething else in the sentence (had, does, will, is known, was known).We call this "something else" a time marker.
However, not every infinitive refersto the same time as that expressed by the time marker.
He is believed never to have smiled at anyone. (= Peoplebelieve he (has) never smiled at anyone.)
He was believed never to have smiled at anyone. (= People believed he had neversmiled at anyone.)
To have smiled refers to an earlier time than that of the time marker. Thesame applies in the case of certain modals:
It may have been David. (= It is possible that it wasDavid.)
You shouldn’t have behaved in such a way. (= It is wrong that you did so.)
There are four types of infinitives.Each has an active and a passive form.

	active	passive
simple infinitive	(to) write	(to) be written
perfect infinitive	(to) have written	(to) have been written
continuous infinitive	(to) be writing	(to) be being written°
perfect continuous infinitive	(to) have been writing	(to) have been being written°

Did you write your name on the application? (write refers to the time of did)
You ought to have written to her. (have written refers to a timeearlier than that of ought to)
I’d rather be writing my thesis now. (be writing refers to thetime of would and expresses a continuous action)
He was said to have been writing that song for ten years. (have beenwriting refers to a time earlier than that of was and expresses acontinuous action)
Your composition has to be written by hand.
This sonnet must have been written by Shakespeare.
A new novel is believed to be being written by Paul Auster. °
This strange and incomprehensible sentence is rumoured to have been beingwritten while the authors were very very depressed. °
°rarely used

应该选D.
1. "be thought"是被现在的人认为，所以用is而不是was。
2.be thought/known to have done是一个好的表达，表明done的事情发生在过去，并不是表示完成。举个例子：
如果用It is known造句：It is known that Edison invented electronic light bulbs in 2000.
如果把这个句子改称be known to的形式就要用: Edison is known to have invented electronic light bulbs in 2000.
3. ABC中说现存所有“染色体”是从一个“人”繁衍下来的，是不合逻辑的。
4.C和E用whom指代ancestor是错的，因为ancestor在句子作主语，必须用who.

-- by 会员 松鼠gg (2009/7/16 9:49:00)

winow

神奇的语法现象。

lelezhang1

清晰明了！！！

jayhung

所有格里的人不能被who指代，所以AB错，C的话染色体不能和祖先对应，E的话it的指代不清，was thought说的好像是在140000年前被以为，而且D的be thought to have done用的很好，见如下
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。（摘自某大神）