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 a roof's job is just to keep rain out, but in cities, rain becomes a problem. When it falls on concrete and asphalt, it can't soak in. Instead, it runs off quickly, overwhelming storm drains and causing floods. Green roofs, which are covered with soil and plants, absorb rainwater like a sponge. In fact, a study in Portland found that a typical green roof can hold back up to 70% of the rainfall during a heavy storm. That water is released slowly over hours, which reduces the peak flow into the drainage system. But there are other benefits too. Green roofs also insulate buildings, cutting energy costs by up to 25%. And they create habitats for birds and insects in dense urban areas. However, they're not cheap to install, and they require regular maintenance. Some cities now offer tax breaks to encourage their use, but the initial cost remains a barrier for many building owners.
❓ 题目 What is the main point the professor makes about green roofs?
A. A) They are too expensive to be practical in most cities.
B. B) They help reduce urban flooding by absorbing rainwater.
C. C) They provide better insulation than any other roofing material.
D. D) They are primarily used to create habitats for urban wildlife.
✅ 正确答案
B) They help reduce urban flooding by absorbing rainwater.