tt gwd1-20

1-Q20:

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：D

刚刚开始做gwd。这道题我选的是c.

d中的overcome 和fell 两个动词在一个句子不合理呀

希望各位帮帮忙：）

"overcome" has past tense "overcame" and past participle "overcome"

"fall" has past tense "fell" and past participle "fallen"

C is wrong since it must be symmetric before "and" and after "and" if assume using past perfect tense is correct in this question. 

D is correct since "overcome" is pp to modify birds and past tense "fell" is the predicate.