In the mid-1970s, 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 reducedb) 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 reducec) 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 reducedd) birds overcome by pollution routinely fell from the sky above los angeles freeways, prompting officials in california to devise a plan to reducee) 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