大全-11-16

16.   Because natural gas is composed mostly of methane, a simple hydrocarbon, vehicles powered by natural gas emit less of certain pollutants than the burning of gasoline or diesel fuel.

(A) less of certain pollutants than the burning of gasoline or diesel fuel

(B) fewer of certain pollutants than burning gasoline or diesel fuel do

(C) less of certain pollutants than gasoline or diesel fuel

(D) fewer of certain pollutants than does burning gasoline or diesel fuel（E）

(E) less of certain pollutants than those burning gasoline or diesel fuel

I choose D, but hte answer is E. why?

1) How can "less" modify "pollutants"?

2) "those" in E refers to what?

首先说第二个吧，those 指 the vehicles, 前后都是车才能比较。 

1、less/more of + 可数/不可数。在longman有两个例句： The map covered less of the area than I'd thought.   Flying is less of a risk than driving。

PS：说一点题外话，如果直接用emit less pollutants , 网上找到一句“ They find that ethanol- blended fuel cars are producing no less pollutants than normal gasoline cars, according to an unpublished federal report made available to Canadian Broadcasting Corporation (CBC).”，还有其余的几篇论文也这样用，当然也有emit fewer这么个说法，这个估计都可以吧。

也有人说这里指的是pollutants程度上的差异，而不是pollutants的种类，所以不可数，也有一定道理。如果从做题的角度看只要把握前后可比就可以了。

Ryoking, Thanks a lot for your detailed explanation!

Yes, "those" refers to "vehicles"! This is PARALLELISM, one of the most important GMAT rules.

Therefore, although "less" is not preferred, we still choose E, which is the only choice contains "those"!