完成时的问题，还得问...估计不少人也有这个疑问，牛人们帮忙给个解释吧。

alandiyer

本帖不谈别的就说OG对现在完成时的解释。
10.Carnivorous mammals can endure what would otherwise be lethal levels of body heat because they have a heat-exchange network which kept the brain from getting too hot.
(C) which has kept
关于C用完成时错，OG的解释是has kept indicates a more definite context and time period and suggests that the heat-exchange network may no longer have this effect.
OG认为，has kept 暗示了更明确的语境和时间，并且提出换热网络可能不再有这样的作用了。（动作完成了，不再发生了）

73.Combining enormous physical strength with higher intelligence, the Neanderthals appear as equipped for facing any obstacle the environment could put in their path, but their relatively sudden disappearance during the Paleolithic era indicates that an inability to adapt to some environmental change led to their extinction.
(B)appear to have been equipped to face any obstacle the environment could put in their path,
OG对于选择完成时态的解释是Because Neanderthals “disappeared,” the verb describing their apparent abilities cannot be present tense, so as equipped must be changed to to have been equipped. the expression equipped to face is clearer and more direct than equipped for facing.
OG认为，因为N消失了， 所以其他们所具备的能力也必然消失了，所以应该用完成时（该动作完成，且不再发生）

74.A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities had been allowed to dump into the Great Lakes.(A)reduced the amount of phosphates that municipalities had been allowed to dump
OG对完成时的解释Since the dumping continued after the date of the agreement, the past perfect verb had been allowed should instead be the present are allowed(if the agreement remained in e?ect when the sentence was written) or the past were allowed (if the agreement was no longer in e?ect when the sentence was written)
OG认为在该协议生效之后，倾倒行为还在持续，所以要用现在时，（用完成时表示该动作已经结束，不再发生）。

在此做个小结，现在完成时可以有以下两个作用  ---------摘自manhatton
1. 动作发生在过去，持续到现在。（continued action）
Right: This country HAS ENFORCED strict immigration laws for thirty years.
Right: They HAVE KNOWN each other since 1987.                                                  
In each case, the idea of "continuing action" is reinforced by a time phrase, such as for thirty years or since 1987, that states how long the action has been occurring.
2. 动作发生在过去，且已经结束并且不再发生，但其影响仍然持续至今。（continued effect of a completed action）
Right: The child HAS DRAWN a square in the sand.
In this example, the child is no longer drawing a square. The act of drawing is finished.
However, the square must still be here somehow; the effect of the act is still operative. If the
square has disappeared, you should use Simple Past.

Clear?
问题还没完。

97.Unlike Schoenberg’s 12tone system that dominated the music of the postwar period, Bartók founded no school and left behind only a handful of disciples.
(D)the 12-tone system of Schoenberg that has dominated
这里完成时的用法的确是不合适的，但是OG的解释同样也有些puzzling，LZ愚钝，木讷...（此处省略一万个字）
OG解释：perfect verb form has dominated distorts the meaning by indicating that the system continues to dominate music today.
完成时暗示该系统至今仍然持续主导地位。。。

想想刚刚的总结
1. 动作发生在过去，持续到现在。（continued action）
此处有for或者since那种表示延续性概念的时间状语吗？木有啊，为鼠磨能持续到today呢？
2. 动作发生在过去，且已经结束并且不再发生，但其影响仍然持续至今。
解释说的是完成时表示12tone system 仍然dominate至今，（注意不是影响持续至今）明显OG解释不是用这一点解释的。

LZ刷OG时态纵向时候发现这个解释，LZ看到这个解释，瞬间石化。。。击碎了楼主之前关于现在完成时的总结。。。
不能理解，贴题于此，请牛牛们，帮忙分析。。。看在LZ三点还写这么长的帖子的份上。。。

babybearmm

首先，建议看以下整个讨论，关注Ron的贴子
http://www.beatthegmat.com/present-perfect-and-past-perfect-usage-summarized-t49438.html
http://www.manhattangmat.com/forums/post58397.html#p58397
另外Stacey这篇，包括后面Q&A：
http://www.beatthegmat.com/mba/2012/02/05/more-on-meaning-a-gmatprep-sentence-correction-problem
看完之后就crystal clear了，我目前对时态的理解基本都是基于Manhattan和以上文章，供参考。

其实时态之所以难，就难在除了基本的rules之外，还有implied meaning.
用中文打个比方，如果老师的评价是“该生学习努力”，那蕴含的意思就是该生成绩并不出类拔萃（但这孩子挺努力的），否则就会说“该生学习成绩优异”。
你下面列举出来的例子，有的OG解释就属于错误时态有错误的implied meaning.

完成时也是这样的道理，甭管present perfect，还是past perfect，都是一个道理。两种情况：
1. 事情持续到 现在时间点(present perfect)/过去时间点(past perfect)
2. 事情虽然结束，但是对 现在(present perfect)/过去(past perfect) 时间点上的事件产生直接影响(direct bearing)
你后面的总结很正确。
有同学理解不了第2点，我在这里有解释
http://forum.chasedream.com/GMAT_SC/thread-670346-1-1.html
学术论文里经常出现"revious studies have shown that ...."就是这个道理。
这点我觉得需要特别注意。
另外据说在时态上，American English跟British English有细微差别（话说，高中老师怎么教的，xdf怎么教的，我不知道....），所以丢掉高中那一套吧。

plz see below for my comments

本帖不谈别的就说OG对现在完成时的解释。
10.Carnivorous mammals can endure what would otherwise be lethal levels of body heat because they have a heat-exchange network which kept the brain from getting too hot.
(C) which has kept
关于C用完成时错，OG的解释是has kept indicates a more definite context and time period and suggests that the heat-exchange network may no longer have this effect.
OG认为，has kept 暗示了更明确的语境和时间，并且提出换热网络可能不再有这样的作用了。（动作完成了，不再发生了）

这题正确答案：
Carnivorous mammals can endure (what would otherwise be lethal levels of body heat) because they have a heat-exchange network that keeps the brain from getting too hot.
整个这句话描述一般自然规律，肯定用simple present tense. 注意主句里，黑体的几个动词时态一致。
OG说得没错，"has kept"有implied meaning.....

73.Combining enormous physical strength with higher intelligence, the Neanderthals appear as equipped for facing any obstacle the environment could put in their path, but their relatively sudden disappearance during the Paleolithic era indicates that an inability to adapt to some environmental change led to their extinction.
(B)appear to have been equipped to face any obstacle the environment could put in their path,
OG对于选择完成时态的解释是Because Neanderthals “disappeared,” the verb describing their apparent abilities cannot be present tense, so as equipped must be changed to to have been equipped. the expression equipped to face is clearer and more direct than equipped for facing.
OG认为，因为N消失了， 所以其他们所具备的能力也必然消失了，所以应该用完成时（该动作完成，且不再发生）

这题因为有appear，正常情况下是"appear to do"对不对？或者说"appear to be"，但为了简洁，把"to be"省略。
He appears an idiot.
He appears to have Neurodegenerative Diseases.
这是现在时的appear的情况。那么咱要说从现在看，过去的东东咋样，就应该从时态上“退位”一步。因为appear后面只能跟不定式to do/be，你不能说
"appear to did/was/were"，那怎么办呢？就只好说"appear to have been" "appear to have done"，就这个道理啦。
Dinosaurs appear to have been relatively smart.

74.A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities had been allowed to dump into the Great Lakes.(A)reduced the amount of phosphates that municipalities had been allowed to dump
OG对完成时的解释Since the dumping continued after the date of the agreement, the past perfect verb had been allowed should instead be the present are allowed(if the agreement remained in e?ect when the sentence was written) or the past were allowed (if the agreement was no longer in e?ect when the sentence was written)
OG认为在该协议生效之后，倾倒行为还在持续，所以要用现在时，（用完成时表示该动作已经结束，不再发生）。

哈哈这题经典，必须从意思上去理解。事件("be allowed to dump phosphates")随时发生，而这个协议呢，是进行量的限制。（过去dump phosphates，现在也会dump phosphates。）所以用"are allowed"
我们假设这个协议变一下：过去能dump phosphates，这个1972年的协议说：“从今以后禁止dump phosphates”。那么这句话就要写成：
1972 agreement between Canada and the United States forbade dumping phosphates that municipalities had been allowed to dump into the Great Lakes.
注意，这个时候，就该用"had been allowed"，表示在过去时间点(1972协议生效）之前发生的、之后不存在的事情。

在此做个小结，现在完成时可以有以下两个作用  ---------摘自manhatton
1. 动作发生在过去，持续到现在。（continued action）
Right: This country HAS ENFORCED strict immigration laws for thirty years.
Right: They HAVE KNOWN each other since 1987.                                                  
In each case, the idea of "continuing action" is reinforced by a time phrase, such as for thirty years or since 1987, that states how long the action has been occurring.
2. 动作发生在过去，且已经结束并且不再发生，但其影响仍然持续至今。（continued effect of a completed action）
Right: The child HAS DRAWN a square in the sand.
In this example, the child is no longer drawing a square. The act of drawing is finished.
However, the square must still be here somehow; the effect of the act is still operative. If the
square has disappeared, you should use Simple Past.

Clear?
问题还没完。

97.Unlike Schoenberg’s 12tone system that dominated the music of the postwar period, Bartók founded no school and left behind only a handful of disciples.
(D)the 12-tone system of Schoenberg that has dominated
这里完成时的用法的确是不合适的，但是OG的解释同样也有些puzzling，LZ愚钝，木讷...（此处省略一万个字）
OG解释：perfect verb form has dominated distorts the meaning by indicating that the system continues to dominate music today.
完成时暗示该系统至今仍然持续主导地位。。。

你没有给出正确句子......这题正确的句子是：
Unlike Schoenberg, whose 12-tone system dominated the music of the postwar period, Bartók founded no school and left behind only a handful of disciples.
看吧，"the postwar period"显然是一个过去的period，所以用dominated.

想想刚刚的总结
1. 动作发生在过去，持续到现在。（continued action）
此处有for或者since那种表示延续性概念的时间状语吗？木有啊，为鼠磨能持续到today呢？
2. 动作发生在过去，且已经结束并且不再发生，但其影响仍然持续至今。
解释说的是完成时表示12tone system 仍然dominate至今，（注意不是影响持续至今）明显OG解释不是用这一点解释的。

LZ刷OG时态纵向时候发现这个解释，LZ看到这个解释，瞬间石化。。。击碎了楼主之前关于现在完成时的总结。。。
不能理解，贴题于此，请牛牛们，帮忙分析。。。看在LZ三点还写这么长的帖子的份上。。。

-- by 会员 alandiyer (2012/2/29 2:58:59)

liulu007

baby解释的好详细哦。

alandiyer

首先，建议看以下整个讨论，关注Ron的贴子
http://www.beatthegmat.com/present-perfect-and-past-perfect-usage-summarized-t49438.html
http://www.manhattangmat.com/forums/post58397.html#p58397
另外Stacey这篇，包括后面Q&A：
http://www.beatthegmat.com/mba/2012/02/05/more-on-meaning-a-gmatprep-sentence-correction-problem
看完之后就crystal clear了，我目前对时态的理解基本都是基于Manhattan和以上文章，供参考。

其实时态之所以难，就难在除了基本的rules之外，还有implied meaning.
用中文打个比方，如果老师的评价是“该生学习努力”，那蕴含的意思就是该生成绩并不出类拔萃（但这孩子挺努力的），否则就会说“该生学习成绩优异”。
你下面列举出来的例子，有的OG解释就属于错误时态有错误的implied meaning.

完成时也是这样的道理，甭管present perfect，还是past perfect，都是一个道理。两种情况：
1. 事情持续到 现在时间点(present perfect)/过去时间点(past perfect)
2. 事情虽然结束，但是对 现在(present perfect)/过去(past perfect) 时间点上的事件产生直接影响(direct bearing)
你后面的总结很正确。
有同学理解不了第2点，我在这里有解释
http://forum.chasedream.com/GMAT_SC/thread-670346-1-1.html
学术论文里经常出现"revious studies have shown that ...."就是这个道理。
这点我觉得需要特别注意。
另外据说在时态上，American English跟British English有细微差别（话说，高中老师怎么教的，xdf怎么教的，我不知道....），所以丢掉高中那一套吧。

plz see below for my comments

本帖不谈别的就说OG对现在完成时的解释。
10.Carnivorous mammals can endure what would otherwise be lethal levels of body heat because they have a heat-exchange network which kept the brain from getting too hot.
(C) which has kept
关于C用完成时错，OG的解释是has kept indicates a more definite context and time period and suggests that the heat-exchange network may no longer have this effect.
OG认为，has kept 暗示了更明确的语境和时间，并且提出换热网络可能不再有这样的作用了。（动作完成了，不再发生了）

这题正确答案：
Carnivorous mammals can endure (what would otherwise be lethal levels of body heat) because they have a heat-exchange network that keeps the brain from getting too hot.
整个这句话描述一般自然规律，肯定用simple present tense. 注意主句里，黑体的几个动词时态一致。
OG说得没错，"has kept"有implied meaning.....

73.Combining enormous physical strength with higher intelligence, the Neanderthals appear as equipped for facing any obstacle the environment could put in their path, but their relatively sudden disappearance during the Paleolithic era indicates that an inability to adapt to some environmental change led to their extinction.
(B)appear to have been equipped to face any obstacle the environment could put in their path,
OG对于选择完成时态的解释是Because Neanderthals “disappeared,” the verb describing their apparent abilities cannot be present tense, so as equipped must be changed to to have been equipped. the expression equipped to face is clearer and more direct than equipped for facing.
OG认为，因为N消失了， 所以其他们所具备的能力也必然消失了，所以应该用完成时（该动作完成，且不再发生）

这题因为有appear，正常情况下是"appear to do"对不对？或者说"appear to be"，但为了简洁，把"to be"省略。
He appears an idiot.
He appears to have Neurodegenerative Diseases.
这是现在时的appear的情况。那么咱要说从现在看，过去的东东咋样，就应该从时态上“退位”一步。因为appear后面只能跟不定式to do/be，你不能说
"appear to did/was/were"，那怎么办呢？就只好说"appear to have been" "appear to have done"，就这个道理啦。
Dinosaurs appear to have been relatively smart.

74.A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities had been allowed to dump into the Great Lakes.(A)reduced the amount of phosphates that municipalities had been allowed to dump
OG对完成时的解释Since the dumping continued after the date of the agreement, the past perfect verb had been allowed should instead be the present are allowed(if the agreement remained in e?ect when the sentence was written) or the past were allowed (if the agreement was no longer in e?ect when the sentence was written)
OG认为在该协议生效之后，倾倒行为还在持续，所以要用现在时，（用完成时表示该动作已经结束，不再发生）。

哈哈这题经典，必须从意思上去理解。事件("be allowed to dump phosphates")随时发生，而这个协议呢，是进行量的限制。（过去dump phosphates，现在也会dump phosphates。）所以用"are allowed"
我们假设这个协议变一下：过去能dump phosphates，这个1972年的协议说：“从今以后禁止dump phosphates”。那么这句话就要写成：
1972 agreement between Canada and the United States forbade dumping phosphates that municipalities had been allowed to dump into the Great Lakes.
注意，这个时候，就该用"had been allowed"，表示在过去时间点(1972协议生效）之前发生的、之后不存在的事情。

在此做个小结，现在完成时可以有以下两个作用  ---------摘自manhatton
1. 动作发生在过去，持续到现在。（continued action）
Right: This country HAS ENFORCED strict immigration laws for thirty years.
Right: They HAVE KNOWN each other since 1987.                                                  
In each case, the idea of "continuing action" is reinforced by a time phrase, such as for thirty years or since 1987, that states how long the action has been occurring.
2. 动作发生在过去，且已经结束并且不再发生，但其影响仍然持续至今。（continued effect of a completed action）
Right: The child HAS DRAWN a square in the sand.
In this example, the child is no longer drawing a square. The act of drawing is finished.
However, the square must still be here somehow; the effect of the act is still operative. If the
square has disappeared, you should use Simple Past.

Clear?
问题还没完。

97.Unlike Schoenberg’s 12tone system that dominated the music of the postwar period, Bartók founded no school and left behind only a handful of disciples.
(D)the 12-tone system of Schoenberg that has dominated
这里完成时的用法的确是不合适的，但是OG的解释同样也有些puzzling，LZ愚钝，木讷...（此处省略一万个字）
OG解释：perfect verb form has dominated distorts the meaning by indicating that the system continues to dominate music today.
完成时暗示该系统至今仍然持续主导地位。。。

你没有给出正确句子......这题正确的句子是：
Unlike Schoenberg, whose 12-tone system dominated the music of the postwar period, Bartók founded no school and left behind only a handful of disciples.
看吧，"the postwar period"显然是一个过去的period，所以用dominated.

想想刚刚的总结
1. 动作发生在过去，持续到现在。（continued action）
此处有for或者since那种表示延续性概念的时间状语吗？木有啊，为鼠磨能持续到today呢？
2. 动作发生在过去，且已经结束并且不再发生，但其影响仍然持续至今。
解释说的是完成时表示12tone system 仍然dominate至今，（注意不是影响持续至今）明显OG解释不是用这一点解释的。

LZ刷OG时态纵向时候发现这个解释，LZ看到这个解释，瞬间石化。。。击碎了楼主之前关于现在完成时的总结。。。
不能理解，贴题于此，请牛牛们，帮忙分析。。。看在LZ三点还写这么长的帖子的份上。。。

-- by 会员 alandiyer (2012/2/29 2:58:59)

-- by 会员 babybearmm (2012/2/29 9:11:18)

清楚多了，多谢babybearmm。尤其几个链接受益匪浅啊。

亲亲麦小兜

mark

wangjieava23

我也先踩一下，被74弄死了。恩恩，baby 真挺牛。

CCcarol

Mark~~~

mongmong

莽莽要上7

谢谢babe姐姐立马我就又补了自己一漏洞！

pirate舟

关于74题，我之前有一个错误的想法，导致一直觉得a也可以选，现在想清楚一些了，所以也写一下，其他人如果也有我这种问题，可以一看。求指正。

就是这里的 that 从句是修饰的是 phosphates， 而不是 the amount of phosphates, 因为that 紧跟在phosphates后面。
之前为什么想不通A选项，就是认为如果that限定的是amount的话，那么句子可以理解成：
agreement降低了p的数量，that，p的数量就是（降低之前）m被允许扔去g lakes里面的数量。------这个数量是在reduced这个动作之前m可以扔的，那么用完成时没错。

而事实上，that限定的phosphates，那么这句话的意思其实是：
agreement降低了（m被允许扔到G lakes里面的）p 的数量-----that是括号里限定p的，只要m一直可以扔p去lakes里，就用现在时；如果后来不能扔了，就用过去时。但是完成时无论怎样，都是不能用的。