thanghnvn Wrote:yu.baba2008 Wrote:Hi, all
Please can anybody help me with this sentence correction question:
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
The ans is c but I chose a. Why a is incorrect?Shouldn't "date" be followed with "when"? And is it necessary to use past perfect tense as in choice c? I would like to choose the simple past tense.
Thank you in advance for your kind help~
babayu
in A, "when it is known" must modify "date" and so this is not logic because the date is in the past but "it is known " is in present.
in B, "at which" can modify "it is known" or "human had made". both these modifications are not logic. the date is in the past, it can not be in present or past perfect
in C, "at which" can modify both " human are known" and " to have made" . but "at which" make sense only with " have known". logic. correct.
in D, "the date that" is ungrammatical. we need "at". this case is in spoken english.
in E, "the date of human" make no sense,
I have read through this thread, but i cannot understand:
1/ in choice C, why we don't interpret that "at which " modify "human are known"? on the other hand, in choice A and B, we interpret that "at which " and "when" modify "it is known".
2/ if we use logic and then decide that in choice C, "at which" should not modify "human are known", then why we don't use logic in A and B, logically, "at which " and "when" should not modify "it is known".
Could anyone clarify for me?
many thanks.
Cris