Concept:Natural resources that can be conserved are those that can be protected, managed, or replenished by human effort.
Explanation:Soil can be conserved by terracing, afforestation, and proper farming practices.
Water can be conserved by storing it in reservoirs and using it carefully.
Wildlife can be conserved by establishing game reserves, sanctuaries, and enforcing laws.
Air, however, is a free-flowing gaseous mixture that humans cannot store, manage, or replenish in a limited sense.
Therefore, among the given options, air is the resource that cannot be conserved.
Answer:D. air