求助：GWD31，第一套V20

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请牛人帮解释一下为什么答案选 D。谢谢！！

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.

 

1. 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
2. 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
3. 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
4. birds overcome by pollution routinely fell from the sky above Los Angeles freeways, prompting officials in California to devise a plan to reduce
5. 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

米可可

A中falling和were overcome形式不一致，不能用and

B中were falling，没必要用过去进行时吧，而且it指代不明

C中had been overcome和fell时态不一致

E中overcome如果当谓语要用被动时态，且falling的形式与overcome也不一致，也不能用and连接

不知道这样分析对不对……牛牛们指点一下……

Winbolin

我是直接看畫線尾端 ...plan 應用 to 表示 "達到...目的", ...plan that reduced ...比較沒plan to那麼簡潔

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的确，先看固定词组搭配能省下不少力气。谢过！

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用and的并列结构语态相近就能选出正确答案了，我当时怎么就没有想清楚呢