[問題] GWD SC問題

[izzylf (風)]

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

可以請問一下為什麼是D嗎? 感謝!!

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推 akainorei:用時態就可以解這題了, since是關鍵字
推 akainorei:雖然說我拿到的詳解討論是說這題沒答案或題目可能錯 = =
推 akainorei:因為overcome前面沒有have,感覺反而像現在式而不是完成
→ izzylf:喔!!好!!感謝你^^