Concept: Protecting the physical environment means reducing pollution and preserving natural resources.Explanation:• Recycling waste materials reduces the amount of waste dumped in the environment.• It helps prevent land, water, and air pollution.• It also conserves natural resources by reusing materials.• Drying industrial waste, practicing traditional farming, and redirecting river channels are not the best general ways of protecting the physical environment from waste pollution.Answer: D. recycling of waste materials