Correct the sentence below:
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.

(a) 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

(b) 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

(c) 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

(d) birds overcome by pollution routinely fell from the sky above los angeles freeways, prompting officials in california to devise a plan to reduce

(e) 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