Nghe TOEFL

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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 tidal power. Unlike solar and wind, tidal energy is predictable because it depends on the gravitational pull of the moon and the sun, which we can calculate in advance. However, there are significant challenges. The most common method is building a tidal barrage, which is essentially a dam across a bay or estuary. When the tide comes in, water flows through turbines, generating electricity. But barrages can disrupt local ecosystems. They change the salinity levels and sediment flow, which affects fish and birds that rely on the intertidal zone. An alternative is tidal stream generators, which work like underwater wind turbines. They're less invasive but currently more expensive and harder to maintain due to saltwater corrosion. So while tidal power offers reliability, we must weigh its environmental costs and economic feasibility. Any questions?