Both classes of engines are of very similar construction. But as the higher pressure is called upon in cylinders, it has to be of more substantial construction, and is thus heavier. In general, the diesel engine may weigh about 9.25 kilograms per kilowatt. The most important advantage of the gasoline engine is its lower weight per kilowatt. The gasoline engine for automobiles may weigh about 6.17 kilograms per kilowatt, and gasoline engines for airplanes may weigh as 0.77 kilograms per kilowatt. This advantage prevents the diesel engine form replacing the gasoline engine in some automobiles and airplanes. In addition, the engine runs cooler than the gasoline engine. This advantage is especially obvious at lower speeds. Diesel oil is not only cheaper than gasoline, but also safer to store. What advantage is especially obvious at lower speeds for diesel engines? A. The diesel engine runs cooler than the gasoline engine. B. The diesel engine runs hotter than the gasoline engine. C. The diesel engine runs harder than the gasoline engine.