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.
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Asince 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
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Bsince 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
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Cbirds 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
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Dbirds overcome by pollution routinely fell from the sky above Los Angeles freeways, prompting officials in California to devise a plan to reduce
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Ebirds 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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正确答案: D