Providing initial evidence that airport are a larger source of pollution than they were once believed to be, environmentalists in Chicago report that the total amount of pollutant emitted annually by vehicles at O’Hare International Airport is twice as much as that which is being emitted annually by all motor vehicles in the Chicago metropolitan area.

 

1. as much as that which is being emitted annually by all

2. as much annually as is emitted by the

3. as much compared to what is annually emitted by all

4. that emitted annually by all

5. that emitted annually compared to the

为什么答案是D？ 感觉TWICE WHAT 比较好。

annually和前面的重复了吧，如果是as mush as就对了吧。而且少了all改变了句意了

又看了一遍，明白了。
Providing initial evidence
that airport are a larger source of pollution than they were once
believed to be, environmentalists in Chicago report that the total
amount of pollutant emitted annually by vehicles at O’Hare
International Airport is twice that emitted annually by all motor vehicles in the Chicago metropolitan area.

that 做代词指代amount of pollutant，不是定语从句的that。emitted做后置定语修饰that。

the amount of ...表示数量，不能用as much as