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, you might think that a roof covered with plants would be heavy and expensive, but actually, modern green roofs are designed to be lightweight and cost-effective in the long run. The key is that they absorb rainwater, reducing the amount that runs off into the streets and overwhelms our drainage systems. In a typical city, over 60% of rainfall becomes runoff, but a green roof can retain up to 70% of that water in the summer, releasing it slowly through evaporation and plant transpiration. This not only eases the pressure on sewer systems but also helps cool the building, lowering energy costs. However, there are challenges: the initial installation cost is higher than a regular roof, and the roof must be properly waterproofed to prevent leaks. But many cities now offer tax incentives for building owners who install them. So, while green roofs aren't a silver bullet, they represent a practical, nature-based solution that can significantly mitigate flood risk.
❓ 题目 What is the main point the professor makes about green roofs?
A. They are too expensive to be practical for most urban buildings.
B. They are an effective way to reduce urban flooding by absorbing rainwater.
C. They require regular maintenance to prevent leaks and water damage.
D. They are most useful in cities with low annual rainfall.
✅ 正确答案
They are an effective way to reduce urban flooding by absorbing rainwater.