Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a surprising solution to urban flooding: green roofs. Now, when it rains heavily in a city, the stormwater runs off rooftops and pavement, overwhelming the drainage systems and causing floods. Traditional roofs are impermeable, meaning water just flows off them. But a green roof, covered with vegetation and soil, acts like a sponge. It absorbs rainfall, slows down the runoff, and releases water gradually. Moreover, the plants filter pollutants from the water, improving water quality. Some cities, like Toronto, have even passed bylaws requiring green roofs on new buildings. Of course, there are challenges. The initial cost is higher than a conventional roof, and maintenance is needed. But in the long run, green roofs can reduce the need for expensive stormwater infrastructure. They also provide insulation, cutting energy costs. So, while green roofs aren't a cure-all, they're a key part of sustainable urban design.
❓ 题目 What is the main benefit of green roofs mentioned by the professor?
A. They generate renewable energy for buildings.
B. They absorb and slow down stormwater runoff.
C. They eliminate the need for any drainage systems.
D. They are cheaper to install than conventional roofs.
