Answer:
Main idea
Explanation:
The main idea is the central point which is buttressed by series of details or points that support the purpose of the main idea.
Beowulf went to battle because Grendel attacked a nearby village and the king of that village asked Beowulf for help.
Answer 4 would be the correctly punctuated sentence.
I don't recommend using the first person pronoun in an argumentative essay. Unless your instructor suggests that you do so, omit it from the assignment because your writing will read better without it.