Answer:
The answer is C.
Explanation:
They is a vague pronoun. Proper nouns correct it, and we are talking about both of them.
 
        
                    
             
        
        
        
The poem is about personally inflicted pain due to loss of love (like a breakup) "is there a balm in Gilead?" is actually a Bible reference, Gilead is a part of modern day Jordan, known for it's healing ointment. The narrator is really asking if there is any healing.  The narrator continually asks dark questions of the raven fully knowing that the answer is always, "nevermore" therefore inflicting a sort of mental torture. Some people cut themselves, this guy asks birds what they think. 
(not putting down self harmers, I'm one myself)
        
             
        
        
        
The most descriptive sentence out of your options is C.
This sentence describes what the author wants the reader to see. The other sentence options are just statements without much color or description.
Hope that helps!
-Chris