Answer: D. wetlands
Explanation: Wetlands are often referred to as "biological supermarkets" because they are highly productive ecosystems. They support a diverse range of plant and animal species and provide various ecosystem services. Wetlands are characterized by their high biological productivity, serving as essential habitats for birds, fish, amphibians, and other wildlife. They also help in water filtration, flood control, and carbon storage. Due to their high productivity and biodiversity, wetlands are often considered crucial for both wildlife conservation and human well-being.