Question

Beowulf slays Grendel in order to —

A) save Hrothgar and the Danes from the monster
B) prevent Grendel from invading the land of the Geats
C) keep Herot from being destroyed
D) carry off the treasure in Grendel’s lair

Answer 1

A) save Hrothgar and the Danes from the monster

Answer 2

He slays Grendel to save Hrothgar and the Danes.  Grendal is the antagonist in Hrothgar and Beowulf specifically goes there to help, because he is a hero.  Heroes in mythology have the primary goal of obtaining immortality through the one way a mortal can - being remembered for their deeds.