vikram4689 wrote: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

what is wrong with A

I see three problems with A:

a) use of IT IS KNOWN (use of pronoun without any referent)

b) pushing back by more than 150,000 years the earliest date when xxx.. (it suggests that dates were pushed back only when IT IS KNOWN THAT HUMANS MADE STONE). Look at similar construction

"Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close"

c) In C use of ARE KNOWN and TO HAVE MADE clearly suggests that HUMANS ARE KNOWN TODAY THAT THEY MADE TOOLS IN PAST - same clarity is not there in A

IMO C

patanjali.purpose wrote:
a) use of IT IS KNOWN (use of pronoun without any referent)

The use of "it" as a subject isn't necessarily wrong. For example:

"It is known that dinosaurs died out about 65 million years ago."

In fact, it is fine in A. The problem is that the wording seems to indicate that the date at which it was known that humans made stone tools was pushed back, not the actual date at which they made stone tools:

"pushing back by more than 150,000 years the earliest date when it is known "

Bill,
Bang on I thought exactly the same but then i decided to confirm as i might be wrong..great feeling now.. One more question here - which tense is "is + past participle" e.g. is known , is descended

Patanjali,
is this an official sentence - i can see it is RUN-ON - "Though viewed from a distance, Saturn's main rings may appear to be smooth and continuous, they are in fact composed of thousands of separate icy ringlets when viewed up close"

vikram4689 wrote:Bill,
Bang on I thought exactly the same but then i decided to confirm as i might be wrong..great feeling now.. One more question here - which tense is "is + past participle" e.g. is known , is descended

I'd say present tense. For example:

Australian embryologists have found evidence that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolved as a kind of snorkel.

We are talking about the elephant today having come from an aquatic animal.

thanks... how different would it be from "the elephant is a descendant of an aquatic animal", actually i am not clear on function of "descended", so i am trying to relate it to construction i know

Also, what would be the correct tense for mentioning a reported instance e.g. he said that (...) tense in the (...) should be past tense or past perfect

vikram4689 wrote:thanks... how different would it be from "the elephant is a descendant of an aquatic animal", actually i am not clear on function of "descended", so i am trying to relate it to construction i know

It is expressing the same idea. Either would be fine, as far as I'm aware. In the original example, "descended" is used as an adjective: the elephant has the quality of being descended from an aquatic animal.

Also, what would be the correct tense for mentioning a reported instance e.g. he said that (...) tense in the (...) should be past tense or past perfect

Can you be more specific? In general, the dependent clause could take many tenses:

Present: He said that I am the best person ever.

Past: He said that you played well yesterday.

Present perfect: He said that you have taken three practice tests so far.

Past perfect: He said that he had re-injured his ankle during the game.

Bill@VeritasPrep wrote: Can you be more specific? In general, the dependent clause could take many tenses:

Present: He said that I am the best person ever.
this is a always statement, so time does not matter

Past: He said that you played well yesterday.
does this mean that playing happened at time t(-1)

Present perfect: He said that you have taken three practice tests so far.
does this mean that 3 tests were taken by the time he said i.e. t(-1) or by the present time i.e. t(0)

Past perfect: He said that he had re-injured his ankle during the game
does this mean that re-injuring happened at time t(-2)

basically i get confused between 2 time instants. Lets say present time is t(0) so saying in "he said that..." happened at time t(-1). Now using this can you help me in above sentences. In each of above sentences, saying happened in time t(-1) but what about time of dependent clause(underlined part). my comments above refer to underlined part only

vikram4689 wrote: [/color]
Past: He said that you played well yesterday.
does this mean that playing happened at time t(-1)

Yep.

Present perfect: He said that you have taken three practice tests so far.
does this mean that 3 tests were taken by the time he said i.e. t(-1) or by the present time i.e. t(0)

For him to make that statement, the tests must have been taken by the time he said so. Conveniently, that means that they have also been taken by the present time

Past perfect: He said that he had re-injured his ankle during the game
does this mean that re-injuring happened at time t(-2)

Yup. The injury must have occurred before he told you.