The correct answer is (c). An ecosystem is a system formed by the interaction of a community of organisms with the physical environment. It is an open system, meaning that it exchanges energy and matter with its surroundings. The other options are all correct.
(a) An ecosystem comprises both abiotic and biotic components. Abiotic components are the non-living parts of an ecosystem, such as air, water, soil, and sunlight. Biotic components are the living parts of an ecosystem, such as plants, animals, and microorganisms.
(b) An ecosystem has its own productivity. Productivity is the rate at which an ecosystem produces new organic matter. It is measured in grams of organic matter produced per square meter per year.
(d) An ecosystem is a natural resource system. Natural resources are the materials and energy that humans use to meet their needs. Ecosystems provide us with many natural resources, such as food, water, wood, and fuel.