In your introductory paragraph, I would define the term "fuel efficient car" for your audience and explain that you want to compare and contrast five different aspects or qualities of fuel efficient cars today. Then devote each paragraph to a single topic, giving the "pros" and cons" of that topic. I don't know what topics you want to use but here are some suggestions: Alternative fuels vs. fossil fuels, Gasoline vs. diesel fuel, Large vs. small engines, Large vs. small vehicles, and Aerodynamics vs. versatility. Within each paragraph you could even give examples of certain vehicles that are or aren't fuel efficient to reinforce your point. Use transition words to move smoothly from one paragraph to the next. At the conclusion of your five paragraphs, summarize the important points that you used to inform your audience and let them be the final judge. Good luck!