Beowulf is battling against evil because he sailed to the Danes to rescue them from Grendel. It is evident in lines 195 onwards to fight Grendel. SO when the night came, Beowulf and his warriors waited in the hall for Grendel to come. Together with his warriors, they sailed to help King Hrothgar defeat Grendel who continued to kill his men.
Yes B is the right answer, to produce a catharsis you are changing the emotion of the readers to show empathy.
