The answer that best fills the blank besides number 4 in the outline is:
D. Conclusion
Whenever one is writing a paragraph, one needs a topic sentence which introduces the topic and the main claim. Then, in a compare and contrast paragraph, one would explain each of the points (as shown in points 2 and 3 of the outline). Finally, in the conclusion one restates the main claim and adds some insight about the topic based on what was discussed throughout the paragraph.