Which energy source is associated with low operating cost and is used for continuous power generation?

• A. Hydro electricity
• B. Nuclear
• C. Combustion engine
• D. Solar

Answer: (A)

The main factor here is long-term operating cost and the ability to provide power continuously. Hydroelectric plants primarily incur maintenance and staffing costs after construction, while the energy source—water—is essentially free. With a dam and reservoir, water can be stored and released to meet demand, allowing near-continuous generation and a high capacity factor. That combination makes hydroelectric power a low operating-cost source that can run continuously, which is exactly what the question describes. In contrast, nuclear involves very high overall costs from safety, regulatory demands, and waste management; solar is very low in fuel cost but is intermittent and typically needs storage or other systems to provide continuous power; combustion engines rely on fuel and have higher operating expenses and less ability to sustain constant output.