Answer: The right answer is the A) Hrothgar felt a strong and unending sorrow that he had no power to overcome. It affected both him and his subjects.
Explanation: Just to elaborate a little on the answer, it can be added that Halfdane’s son was King Hrothgar, the exemplary and famous king of the Danes, whose kingdom had been threatened by the monster Grendel. As a result of that, he felt not just an unending, but also a strong and permanent sorrow ("living sorrow" [...] "simmered, bitter and fresh") that he couldn't get rid of and that "hung" on him and his subjects.