Environmentalist: Discarding old appliances can be dangerous: refrigerators contain chlorofluorocarbons; electronic circuit boards and cathode-ray tubes often contain heavy metals like lead; and old fluorescent bulbs contain mercury, another heavy metal. When landfills are operated properly, such materials pose no threat. However, when landfills are not operated properly, lead and mercury from them contaminate groundwater, for example. On the other hand, when trash is incinerated, heavy metals poison the ash and escape into the air. The environmentalist's statements, if true, most strongly support which one of the following inferences? ['Newer appliances are more dangerous to the environment than older ones.', 'Old fluorescent bulbs should be recycled.', 'Appliances should be kept out of landfills.', 'Appliances containing heavy metals should not be incinerated.']