32.The Chicago and Calumet Rivers originally flowed into the St. Lawrence by way of Lake Michigan, but having been redirected by constructing canals so that the water now empties into the Mississippi by way of the Illinois River.
(A) Rivers originally flowed into the St. Lawrence by way of Lake Michigan, but having been redirected by constructing
(B) Rivers had originally flowed into the St. Lawrence by way of Lake Michigan, but they have been redirected by constructing
(C) Rivers, which originally flowed into the St. Lawrence by way of Lake Michigan but have been redirected by the construction of
(D) Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, but having been redirected by the construction of (E)
(E) Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, have been redirected through the construction of
In E, flowing into the St. Lawrence .... is present tense, however, the rivers have changed their courses. here, i think that it should use a past finished tense. so i choose B.
what wrong with B?
but they have been redirected by constructing，河流是不可能construct什么的
E没错，现在分词修饰完全正确
Further to upstairs, you should note the past perfect tense.
Further to upstairs, you should note the past perfect tense.
我不是很明白在此处,为和用+ING 形式. , originally flowing into the St. Lawrence by way of Lake Michigan,
8. (24773-!-item-!-188;#058&001691)
Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
(A) has long appeared that it was immune from
(B) has long appeared to have been immune from
(C) has long appeared as being immune to
(D) had long appeared immune to
(E) had long appeared that it was immune to
这一题之所以选D，是因为后面的分句用了have now realized，与后面的句子的时态相比，前半句说ozone已经不是这个时候（have now realized的时候）之前的那个时候人们所认识的了，所以用了had long appeared。
那么楼主这道题，为什么B中的时态是错误的？
PREP 的题目是有点大怪路子 啊
虽然同意答案是E,也同意楼上对by v-ing的说法
但是E里面这个分词用的也满奇怪的,原句中用originally flowed , E里面却将谓语动词变成了分词作状语, 似乎有点改变意思的味道
也理解不了什么时候可以把原句子谓语改成插入语。。仍然觉得怪怪的。
支持版主的解释。
此外，此句所要强调的中心意思为后面一句，而非并列强调，仔细体会所要着重强调的中心思想。So that 也表明了强调的中心。
版主关于 by 逻辑主语的总结大部分情况都适用，但我刚找到了一个反例，贴上来一起研究。
prep2
99. (29685-!-item-!-188;#058&004361)
Frederick Winslow Taylor, a machinist and engineer who worked in the early twentieth century,
believed that the productivity of a job could be improved if one were to separate the components of
a task into its individual motions and found the best way to perform each motion, then redesign the
job so that each motion could be done as efficiently as possible.
(A) if one were to separate the components of a task into its individual motions and found the best
way to perform each motion, then redesign
(B) if one separated the components of a task into individual motions, found the best way to perform
the motions, and then redesigning
(C) if the components of a task were separated into individual motions, finding the best way of
performing the motions, and then redesigned
(D) by separating the components of a task into individual motions, finding the best way to perform
each motion, and then redesigning
(E) by separating the components of a task into individual motions, finding the best way of
performing each motion, then redesign
(D)
(D)
by separating, by finding and by redesigning 动作的发出者应该是未提及的人，不可能是the productivity of a job 难道是Frederick Winslow Taylor, 间隔太远了，也有一些牵强。这里 a job 是泛指，所以 by separating, by finding and by redesigning 动作的发出者也应该是泛指的人，而不是 Frederick Winslow Taylor
by separating, by finding and by redesigning 动作的发出者应该是未提及的人，不可能是the productivity of a job 难道是Frederick Winslow Taylor, 间隔太远了，也有一些牵强。这里 a job 是泛指，所以 by separating, by finding and by redesigning 动作的发出者也应该是泛指的人，而不是 Frederick Winslow Taylor
再把这几个例子贴到一起看看
8. (24773-!-item-!-188;#058&001691)
Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
(A) has long appeared that it was immune from
(B) has long appeared to have been immune from
(C) has long appeared as being immune to
(D) had long appeared immune to
(E) had long appeared that it was immune to
这一题之所以选D，是因为后面的分句用了have now realized，与后面的句子的时态相比，前半句说ozone已经不是这个时候（have now realized的时候）之前的那个时候人们所认识的了，所以用了had long appeared。
那么楼主这道题，为什么B中的时态是错误的？
同问。过去完成时为什么错了？谢
我想问E中的被动语态执行者不是不能用through/ as a result表达的吗？
这里为什么是through是对的？
there are two things wrong with (b).
one:
the use of the past perfect (had flowed) is inappropriate, because there is no second past-time marker or event to which this first event is relevant.
compare: the rivers had originally flowed into the st. lawrence, but then their course was diverted by...
the correct tense to use here would be the simple past, because this is the only past time frame referenced in the whole sentence.
two:
'by constructing' seems to refer back to the rivers as its ostensible subject, implying (absurdly) that the rivers themselves constructed the canals.
idiomatically, "BY ___ING" retains the subject of the preceding clause. this is something you just have to know.
it is also something of which most native speakers are aware, even though they can't actually articulate it. (this is the case for a great many, if not most, usage and idiom rules, actually.)
examples:
i am bored by performing jazz --> this means i get bored when i PLAY the music MYSELF.
i am bored by the performance of jazz --> i don't like to sit and listen to someone else play jazz.
hum...
虽然这么说，但是我觉得过去完成时这里其实是有道理的
过去完成时表示1、过去的过去；2、现在完成时的过去
一个例子prep2-8
Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we
have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
(A) has long appeared that it was immune from
(B) has long appeared to
have been immune from
(C) has long appeared as being immune to
(D) had long appeared immune to
(E) had long appeared that it was immune to
注意这题的时态，现在完成时的过去
prep2
99. (29685-!-item-!-188;#058&004361)
Frederick Winslow Taylor, a machinist and engineer who worked in the early twentieth century,
believed that the productivity of a job could be improved if one were to separate the components of
a task into its individual motions and found the best way to perform each motion, then redesign the
job so that each motion could be done as efficiently as possible.
(A) if one were to separate the components of a task into its individual motions and found the best
way to perform each motion, then redesign
(B) if one separated the components of a task into individual motions, found the best way to perform
the motions, and then redesigning
(C) if the components of a task were separated into individual motions, finding the best way of
performing the motions, and then redesigned
(D) by separating the components of a task into individual motions, finding the best way to perform
each motion, and then redesigning
(E) by separating the components of a task into individual motions, finding the best way of
performing each motion, then redesign
看了帖子明白了by的用法。那我想请问 A. 中的 but having being这个用法可以吗？即but后可以跟分词修饰主语吗？
E把原来的限制性定于从句改成了非限制性定于从句没有问题么？
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