LATE to this one here but lets's take a stab at this:
An article revealed one language dies every 14 days because of communities abandoning native tongues in favor of more common ones.
A) one language dies every 14 days because of communities abandoning native tongues in favor of more common ones
B) that one language dies every 14 days due to communities abandoning native tongues in favor of more common ones
C) that one language dies every 14 days because communities abandon native tongues in favor of more common ones
D) one language dies every 14 days because communities abandon native tongues in favor of more common ones
E) the death of one language every 14 days because communities are favoring more common tongues
Ans:
Sentence analysis with breaking down stuff :
An article revealed ( SV pair)
(that)
one language dies every 14 days ( Tell us what article revealed : Uses present tense to state the fact. S-> One language, V-> dies ) ( Fun side note: "that" in parenthesis is skipped by Author - usual writing practice. Would i eliminate an answer based on this - probably not

)
because of communities abandoning native tongues in favor of more common ones. ( Dependent Clause or DC-> explain why language dies. S -> where is it ? Can't find -missing. Verb - where is it ? Missing again

) Communities cannot be subject as it is part of Prepositional phrase ( PP) Or object of prepositional phrase ( technical reason)
DC means to explain why a language dies. It is illogical to say language dies because of communities rather they die because community do something. What do they do ? Communities abandon their native tongue in favour of more common ones. Now the meaning make sense.
Error: DC is big mess : Structure is wrong to convey the intended meaning and SV pair are missing ( though not deal breaker but good to have! )
A) Eliminate for meaning and SV missing
B) Same as A "due to X" X = communities. Sentence has the same core meaning issue as in option A. A language dies not due to communities but because of their action. Eliminate.
C) Nice and clear - conveys intended meaning. Add an additional "that" to clarify what article revealed - hold on
D) Same as C but "that" is skipped. It's hard to choose one over other in C vs D. In C "that" clarifies a bit more and D is more concise.
E) Mess at start. An article revealed "death" ?? No the article revealed a fact that one language dies. An article did not provide proof of death of one language Read further and you find "communities are favouring" - grammatically Ok but minor change in meaning. If communities are favouring that means they have not abandoned so a language must not die. Eliminate
Now if you pick D over C - i would say just a bad luck in my personal opinion. But if i have to choose i will go with C here.

PS: My 2 cents:
Officials questions generally will not be based on such subtle differences and Generis is doing a fantastic job with SC butler project with the question and explanation he post. Send him a big Thank you and Kudos.