Which one of these will go back to how it was?

Materials don’t always stay the same. If you stretch a rubber band, it will bounce back again. But if you chop up a carrot, you can’t put the carrot back together again. When you are baking a cake, the ingredients all look different. But when you mix them together and cook them, they change and become a new material. The cooked cake doesn’t look like any of the ingredients.