Which of the following is an example of an ecosystem service?

The provision of clean air is an example of an ecosystem service because it directly benefits human health and well-being, as well as the overall functioning of the environment. Ecosystem services refer to the benefits that humans derive from natural ecosystems, which include provisioning services (like food and water), regulating services (such as air quality and climate regulation), supporting services (like nutrient cycling and habitat provision), and cultural services (such as recreational and aesthetic enjoyment).

Clean air is a critical regulating service as it is essential for the survival of all living organisms and is inherently linked to natural processes like photosynthesis, plant respiration, and the filtration of pollutants by vegetation and soil. When ecosystems function properly, they help maintain air quality by filtering out harmful substances and providing the oxygen necessary for life.

In contrast, options like construction of buildings, refinement of fossil fuels, and production of plastic are all human-made activities that do not provide the same direct benefits of ecosystem services; instead, they often lead to environmental degradation and can contribute negatively to ecosystems. Therefore, the provision of clean air stands out as an important example of how healthy ecosystems directly support human life and the planet's ecological balance.