这里的 key to ... 是形容词短语作后置定语,意思是“对 ...... 至关重要的",所以不能"把key作名词,在the前加as"。
As roadways choke on traffic, researchers suspect that the tailpipe exhausted from cars and trucks--especially tiny carbon particles already implicated heart disease, cancer and respiratory ailments--may also injure brain cells the key to learning and memory.
最后一句答案给的是key作形容词,删去the。请问key作名词,在the前加as可以吗?