Final answer:
Hydroelectric power generation is an environmentally friendly (Option D) alternative to fossil fuels, producing fewer greenhouse gases but can still impact fish migration and habitats.
Step-by-step explanation:
Hydroelectric power generation is an alternative to fossil fuels that produces fewer greenhouse gases. While it is a renewable source of energy and does not produce emissions of air pollutants during electricity generation, it is not without environmental impacts. Hydropower plants and dams can disrupt fish migration, alter habitats, and displace people, besides potentially causing silting issues. However, hydroelectricity has high acceptance as a clean energy source and contributes significantly to the renewable energy consumption.