Because natural gas is composed mostly

[RonPurewal]

If so, why choice B is incorrect?

"burning x or y" is a singular subject (as are all -ing nouns), so "do" (plural) disagrees with it. you'd need "does" instead.

another example:
Drawing portraits or still-lifes are easier than drawing action scenes.
(incorrect)

Drawing portraits or still-lifes is easier than drawing action scenes.
(correct)

if you understand why the first is wrong and the second is right, then you also understand the issue in (b).

(nb: "still-lifes" is the correct plural of "still-life", even though the plural of "life" is "lives".)

[duyng9989]

What I meant is that if uncountable nouns with "S" or "es" at the end, we use the fewer or many. Else use little or much.

ah, ok, i see what you're saying -- but it isn't quite right.

"fewer" always refers to things that are countable. therefore, if you see the same word used with "fewer" and (in other contexts) with "less", then that word must have two different meanings -- one of them uncountable (referring to a continuous quantity of something), and the other countable (one, two, three, etc.)
as just one example, food can be an uncountable quantity (I eat less food than I did ten years ago.)
but, food(s) can also be a countable quantity, if it refers to different dishes or types of food (I eat fewer foods than I did ten years ago, because I have a better sense of what I like and what I dislike --> this doesn't mean that i eat a smaller amount of food; it means that i eat fewer different types of food.)

if you have to choose between these forms, then there should be adequate context for that decision.
e.g.

* On this diet, you can eat all of the foods you love; you just have to eat less of those foods. --> correct
(you can still eat the whole range of foods; you just need to eat a smaller quantity of each.)

* On this diet, you can eat all of the foods you love; you just have to eat fewer of those foods. --> incorrect
(this sentence is self-contradictory; it is simultaneously saying that you can eat all of the foods and that you can't eat all of them.)

the good news here is that you don't need any sort of sophisticated knowledge to understand this. if there's enough context, then you can make the decision. if there isn't, then look for other decisions that you can make.

Thank you for your previous post. I understand why B is wrong. It is clear now why B is wrong.

I have a question:

If Fewer + Noun countable. Is the noun countable must be in plural form or singular form?

For example: Fewer car or fewer car(s)

(sorry for my stupid basic English question).

Why I ask that is because in your example above, food can be in uncountable and countable form. But it seems to me that the countable form always contain (S). Is that correct?

Fewer + Food (S) not fewer + food (without s)??

Similarly, if a noun has two forms: countable and uncountable. The countable form always contains (s or es) at the end?

Thank you.

I am appreciated your response.

[RonPurewal]

If Fewer + Noun countable. Is the noun countable must be in plural form or singular form?

For example: Fewer car or fewer car(s)

(sorry for my stupid basic English question).

not a stupid question.

always plural. you can't have fewer + singular noun.
on the other hand, if fewer is not directly in front of the noun, then it's possible to come up with situations in which the noun can be singular -- normally, situations in which the singular noun is not the counted object(s) itself, but rather a more general characterization/categorization of that object.

e.g.,
Yesterday I bought more of this type of rivet, and fewer of that type, than I have typically bought in past orders.

this is probably way too much information. but, the answer to your original question (about fewer + noun, directly adjacent to each other) is "always plural".

Similarly, if a noun has two forms: countable and uncountable. The countable form always contains (s or es) at the end?

in most cases it will, but (as is always the case with english) there are exceptions.
for instance, "fish" can be countable (There are 14 fish in the Smiths' aquarium) or uncountable (I eat less fish than I did before, now that I've moved away from the coast).
the problem, though, is that "fish" (countable) is irregular: the singular is fish, and the plural is ... still fish.
(there's also "fishes", which is not quite interchangeable with plural fish, but that distinction is miles and miles beyond the scope of anything that the gmat exam would ever think about testing.)

examples:
I eat less fish than I did before, now that I've moved away from the coast.
(uncountable: say, I eat 8 pounds of fish per year now, whereas I ate 15 pounds of fish per year on the coast. it should be clear, upon consideration, that this sentence is not referring to the number of fish that i ate.)

Ray bought fewer fish this year than last year, because his fish have been living longer lately.
(countable)

i think you get the difference.

but, unless you are looking at a noun that has irregular plural forms (like "fish"), yes, all of the other countable plurals end in -s or -es.

[duyng9989]

Wow.

Very useful. Thank you very much Ron!

So basically, If I see few + noun. I will check if the noun is countable or not. If countable, it, most of the time, must have "s" or "es" at the end.

It is very useful because when I see nouns such as delay, dioxin, gas. If they come with few, they must have "es" or "s" at the end.

Thank you for your useful post.

[jnelson0612]

Very glad that Ron was able to help you. Ron rules! :-)

[vietmoi937]

what is the difference between

fewer of polutants
and
fewer polutants.

I thing they are the same.
what is difference between

less water
and
less of water.

I already understand that "less of polutants" means "a less portion of poluttant.

[RonPurewal]

what is the difference between

fewer of polutants
and
fewer polutants.

I thing they are the same.
what is difference between

less water
and
less of water.

they're not the same, but i don't think this has ever been tested by GMAC.
if you can point to an official problem that actually tests this difference (this one doesn't -- the "of" is in all five choices), i'll take a look.