I do believe the answer is C) American Civil War.
I think the answer would be " C. understanding the author's purpose " because when you annotate something you aren't just describing it , you are formulating an explanation
I believe this is a dependant clause
Since our method of communication wasn't very reliable, I couldn't get enough details. So if you see any mistakes, I apologize. I've tried to fit the criteria you've described, and I hope it works for you.