The final line of the article quotes a passage from booth’s diary, wherein he alludes to the biblical story of cain and abel, the sons of adam and eve. cain, the story goes, killed his brother due to jealousy and anger. what is winik’s point in ending his article with this allusion?

Winik uses this allusion to emphasize that, although Booth sounds as though he is very self-assured, and does not seem to regret what he has done, he ultimately admits to being alone and cursed, as though it was his destiny to do what he did. It seems that Winik believes that his being lonely and feeling wronged is a more accurate reflection of Booth than his otherwise self-confidant demeanor gives on. 

This allusion (in Booth's diary) is also an important factor, in that it indicates that Booth believed his actions were God's will.

"seen" is a past participle that requires a form of the verb "to have" as an auxiliary verb - so we have b) and c) as options.

among the two b is wrong: "has" is a third person form, not a first person form.

c is the correct option.