gwd SC 请教

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

答案是D。

E有什么错？同时D改变了原句的主从关系。请教。

请楼主在标题里面给出题目出处与题号，方便大家回帖，方便后人查询，谢谢啊

不知LZ是否已查询过讨论连接，如已查询请在标题中标明。谢谢配合。

楼上说的是~

这一现象让专家。。。而不是鸟让专家。。。