The correct answer is C.
Grendel gets stuck in a tree trunk and is later on find by humans. When they speak, Grendel realizes he understand the language they use, altough it sounds a little differently.
When the humans talk about bringing Grendel, who must be a tree spirit, food, he laughs very loudly, and they think he is angry, so they become scared of him and try to attack him.
Grendel tries to communicate with them and explain what happened, but they do not understand and become even more scared of him.