Which of the following energy sources is classified as renewable?

Wind energy is classified as a renewable energy source because it harnesses the natural and continuous flow of air through the Earth's atmosphere. Wind power is generated by wind turbines that convert the kinetic energy of wind into electricity. This process does not deplete resources, as the wind is naturally replenished and will continue to flow as long as the sun shines and the Earth rotates.

In contrast, the other energy sources mentioned are non-renewable. Coal and natural gas are fossil fuels formed from ancient organic matter and take millions of years to form, which makes them limited in supply. Once used, they cannot be replaced within a human timescale. Nuclear energy, while not a fossil fuel, relies on uranium, which is finite and has environmental concerns associated with waste management. Thus, wind is the correct answer as it offers a sustainable solution for energy needs without the drawbacks tied to depletion and environmental damage associated with non-renewable energy sources.