单选题 Wood is a readily available and beautiful building material that is preferred by many for home construction. Fire insurance rates on wooden houses are higher than on brick houses or houses made of some other materials. One chemical company advertises a wood treated with noncombustible chemicals. At temperatures below the ignition point of wood, the chemicals react to produce carbon dioxide and water, which choke flames and prevent the spread of fire. In a sense, the treated wood has a ______