Some thermal mugs have layers of materials to keep drinks hot for as long as possible. Which combination of layers would work best for this purpose? A. Inner core of steel, no air gap, outer layer of glass B. Inner core of steel, air gap, outer layer of plastic C. inner core of steel no air gap outer layer of glass D inner core of steel no air gap outer layer of plastic DONT ANSWER IF U DONT KNOW DO NOT GUESS THIS IS FOR A GRADE