The correct answer is A) Grendel's mother.
After he defeats Grendel, Beowulf fight against Grendel's mother.
In the story of Beowulf, Grendel is a prowling monster that terrorizes people and villages. The hero Beowulf decides to confront the monster and goes to the Danes region and fight the monster. He received some help from the King of Hrothgar and the hero fights and kill the monster. After he defeats Grendel, Beowulf fight against Grendel's mother, another demoniac monster.