Its primary purpose is to tell a story. Exposition presents the facts about a subject or an issue as clearly and impartially as possible. Its primary purpose is to explain. The author uses the techniques of persuasion to establish the truth of a statement or to convince the reader of its falsity. The purpose is to persuade the reader to believe something and perhaps to act on that belief.
Argument takes sides on an issue.
Its primary purpose is to convince. Evaluate the book for interest, accuracy, objectivity, importance, thoroughness, and usefulness to its intended audience. Show whether the author's main arguments are true. Respond to the author's opinions. Illustrate whether or not any conclusions drawn are derived logically from the evidence.