Answer: D. Every human has the potential to be either a monster or a person.
Explanation:
We should note that Grendel looked like a monster. Grendel was referred to as a ogre as it kills prey at night as it drank human's blood after killing them.
Grendel was eventually killed by Beowolf. Therefore, the statement that Grendel most likely agree with, based on his outlook on life will be that as humans we can either be a monster or a person.