In the mid-1970's, since birds were overcome by pollution, and routinely falling from the sky above Los Angeles freeways, this prompted officials in California to devise a plan that reduced automobile emissions.


since birds were overcome by pollution, and routinely falling from the sky above Los Angeles free ways, this prompted officials in California to devise a plan that reduced

since birds that had been overcome by pollution were routinely falling from the sky above Los Angeles freeways, it prompted officials in California to devise a plan that would reduce

birds had been overcome by pollution and routinely fell from the sky above Los Angeles freeways, prompting officials in California to devise a plan that reduced

birds overcome by pollution routinely fell from the sky above Los Angeles freeways, prompting officials in California to devise a plan to reduce

birds overcome by pollution and routinely falling from the sky above Los Angeles freeways were prompting officials in California to devise a plan to reduce

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题目分析：
本题在很多个动词上都考查了外延和内涵这一个重要的考点。咱们现在用选项分析一个一个地检查。

选项分析：

A选项：本选项有三处错误。
第一，没有主句，我们可以发现，在选项中间有一个连词and， 那么在它身前有一个句子，谓语动词为overcome，其身前有一个连词since，在and身后的句子中，falling可以作为伴随状语，谓语动词为prompt， 这会使得两个谓语动词被两个连词所连接，让本选项没有了主句；
第二，划线部分最后出现了a plan that reduced automobile emissions。我们应该将定语从句that reduced automobile emissions改为不定式短语to reduce automobile emissions，这点考查了不定式和从句的区别。用之于本题，由于减少机动车的排放是一个计划的目的，即，reduce automobile emissions这个行为是主观性的，能被控制而发生的，应该用不定式短语。
另外，本题中“促使（prompt）”的主语用了this，它可以单独做一个代词。但在逻辑上，由于发出prompt的应该是复数名词birds，至少应改为these。

B选项：本选项有三处错误：
第一，fall的时态有误，应该用过去时而不是过去进行时。
第二，“计划”身后应该用不定式短语来做定语而不是用定语从句，该错误同(A)。
第三，代词it的指代对象有误同选项(A)。

C选项：首先，本选项中birds had been overcome by pollution和routinely fell from the sky above Los Angeles freeways是并列句的关系。但在逻辑上，这两句显然无法并列，应该让overcome句做鸟的定语。plan身后应该用不定式短语做定语，该错误同(A)。

D选项：Correct. 本选项在语法和逻辑上均是正确的。其中现在分词短语prompting officials in California to devise a plan是伴随状语。

E选项：overcome by pollution是过去分词短语，routinely falling from the sky above Los Angeles freeways是现在分词短语，两者在语法上可以由and连接表示平行。但是，在逻辑上，这两句并没有并列关系，该错误同(C)；prompt不应用过去进行时。

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