Providing initial evidence that airports 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 the O'hare International airport is twice as much as that which is being emitted annually by all motor vehicles in the Chicago Metro area

A) as much as that which is being emitted annually by all
B) as much annually as is emitted by the
C) as much compared to what is annually emitted by all
D) that emitted annually by all
E) that emitted annually compared to


Between B and D. Can someone please explain the parallelism error in B.