The correct answer is A: It emphasizes the finality of the captain’s death. This line is used to build tension in the poem, and is later used to describe the captain's death, upon which the speaker mourns and anguishes. The reason why I DON'T THINK that it is B is because the anguihing is not in the moment of the events occuring when the refrain "Follen cold and dead" is stated. It is certainly not C or D, but it could be B. Take a gamble, but I think that it is A beuase of what I stated above.
I hop this helps!