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题库 / Prep2008E1-SC-256
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.
when it is known that humans made
at which it is known that humans had made
at which humans are known to have made
that humans are known to be making
of humans who were known to make
题目分析：
本题相对来说比较难，有几个选项较难排除。
选项分析：
A选项：本选项是一个主语从句，句首的it是形式主语，还原为正常语序则有：
that humans made stone tools is known.
由于整个划线部分是一个定语从句，所以若将先行词补进来则有：
that humans made stone tools at the earliest date is known.
但实际上，本选项至少需要改为：
for humans to have made stone tools at the earliest date is known.
为什么一定要在主句部分用不定式短语呢？这点考查了不定式和从句的区别。用之于本题，本选项的意思是，人们知道的人类最早制造石器的时间（区别于be known for，那个是著名于…的意思，be known to do是被知道…的意思）。此时的know是看法类动词，被动语态下，看法类动词的约束力较强，宾语部分需用不定式的形式。（实际上，和我们高中学习的内容不同，在英语正规的文献中，很少有it is known that的形式，基本都是xxx is known to be，原因就是本选项所写的内容）
B选项：本选项错误同(A)。
C选项：Correct.本选项在语法和逻辑上均是正确的。
D选项：此处用了关系词that，最好改为at which或者是when，这是因为先行词 the earliest date应在定语从句中做状语；另外，to be making应改为to have make。不定式或分词短语中加have表示这件事是先发生于其主句的，即先时性，而加be表示是和主句同时发生的，即，同时性。显然地，在逻辑上，制造石器应该先发生于know这个事件。
E选项：of引导了一个所有格，也可以看作the earliest date的限定性定语。但是，此定语的核心词不正确。在之前的所有选项中，the earliest date定语部分的核心词均为动词know，本选项中核心词为humans（后面的是humans的定语从句）。在逻辑上，最早的时期应该是一件事的日期，而不是“人”的日期。
m
xxx is known to be
humans are known to have made
而不是it is known that
be known for，那个是著名于…的意思，be known to do是被知道…的意思
在英语正规的文献中，很少有it is known that的形式，基本都是xxx is known to be，原因就是本选项所写的内容）
AB ：在earliest date时候，（当时的人们）已经知道人类制造石器
C ：（现在的人们）认为人类在earliest date已经制造石器了
xxx is known to be
A选项：主语主语从句，变成human made tools known 错
A项： 变成了human made tool is know in the earliest date, 错
the earliest date when it is known that humans made stone tools有歧义吧，
可以被理解为that humans made stone tools is know at the earliest date
要知道的是humans made stone tools 的时间，不是humans made stone tools 被known的时间
应该为“人类已知的制作石质工具的年代被提前”
而非“人类制作石质工具被获知”
be known to have done sth的问题：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。
①remember this as an idiomatic usage of the construction \"known to\". if the action is in the present, then you use \"known to VERB\"; if the action is in the past, then you use \"known to have VERBed\". as far as i know, these are the only two possible forms.
②date to/at区分
1) date….to 可追溯sth到...几年，强调发生的时间点，后面是ago
2) date….at 年代判定、鉴别/年份有….年之久，强调发生到现在经过的时间有多长，后面是old
注意体会AB的intended meaning不一样了
pushing back by more than 150,000 years the earliest date /when it is known that humans made stone tools./
将/知道了人们制作石头工具的的日期/推迟 注意体会这个it is known that...
AB 与C 不同的语义区别
AB ：在earliest date时候，（当时的人们）已经知道人类制造石器
C ：（现在的人们）认为人类在earliest date已经制造石器了
Ron I'm pretty sure that either "when" or "at which" would be acceptable. i think (not 100% sure) that "the date when" is used for actual, precise calendar dates, whereas "the date at which" is used for the usually more vague dates of historical events, such as the one in this problem. But i'm sure the test is not going to depend on this sort of nuanced difference.
be known to have done sth的问题：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。 这个解释我觉得好理解点，约束力这种概念太模糊了
CD的区别，to have done 和 to be making考察的是
先时性和同时性的知识点
zei j8 nan
It is known" can't apply to past dates
A 选项指的是在那个时间知道了一个事实 不符合本意 C 选项主语是人 表示the toolmaking happened at that date, and the fact is known now
A的when是可以接受的但是it is known说的是我们知道事件的时间，不是made tools的时间
D 此处用了关系词that，最好改为at which或者是when，这是因为先行词 the earliest date应在定语从句中做状语
be known to have done sth的问题：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