Government of laws and stuff
From my my experience this usually differs depending on the type of book it is, but I think the best choice is either A, to help the reader understand new concepts, or C., It allows the reader to focus on key ideas and information during the reading. I'd pick C though, since it's more in depth and makes more sense.
B. doesn't make that much sense unless the book is an argumentative or a persuasive book.
D. only applies to personal narratives. Nobody can understand a writer's personal experiences and attitudes otherwise.
Whats the question exactly?
My biggest fear is balloons.
I have a fear of balloons but not just looking at them, No No No. When they pop, fly away, or if I touch them that is what triggers my fear. At birthday parties I stay away from them and never have any at my own.
I would say it is C, if not possibly B.