Question

how can unfertile soil be rejuvenated and put to economic use?

• mine for oil and natural gas
• plant and harvest soybeans
• culture and transplant photosynthetic microorganisms
• grow and process algae

Explanation:

Soybeans are legumes that form symbiotic relationships with nitrogen-fixing bacteria (Rhizobium) in their root nodules. These bacteria convert atmospheric nitrogen into a form usable by plants, which enriches the soil with nitrogen—an essential nutrient for fertility. Harvesting soybeans provides economic value, while their growth naturally rejuvenates infertile soil by increasing nitrogen content. Other options do not directly rejuvenate soil: mining depletes resources, photosynthetic microorganisms and algae do not fix nitrogen to improve soil fertility for long-term agricultural use.

Answer:

plant and harvest soybeans