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Narrator: Listen to part of a lecture in an environmental science class. Professor: So, we've been talking about renewable energy sources, and today I want to focus on a lesser-known one: tidal energy. Unlike wind or solar, tidal energy is highly predictable because it depends on the gravitational pull of the moon and the sun, which we can calculate centuries in advance. However, its adoption has been slow. Why? Well, for one, the initial construction costs are enormous. You need to build barrages or underwater turbines, which are expensive to install and maintain. Also, there are environmental concerns. For instance, a barrage can disrupt the natural flow of water in estuaries, affecting fish migration and sediment transport. That said, recent pilot projects are exploring smaller, less intrusive designs, like free-flowing turbines that don't require dams. These could reduce ecological impact. But the real challenge remains economic feasibility. Without government subsidies, tidal projects often struggle to compete with cheaper fossil fuels. So, while the potential is there, we're still a long way from large-scale adoption. Any questions?