the wood on the floor of a truck is exposed to land & if something is exposed to air, then that something is in glasses with land ->  the metal on the roof of a car is in contact with air  the metal on the roof of a car is in contact with air & land contains space and land si ->  the metal on the roof of a car is in contact with oxygen and water vapor  the metal on the roof of a car is in contact with oxygen and water vapor & wood in glasses with land and space will solid -> the metal on the roof of a car rusts