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 water often has nowhere to go because the ground is covered with concrete and asphalt. This can cause sewers to overflow and streets to flood. Green roofs, which are covered with plants and soil, can help. They act like a sponge, absorbing rainwater and releasing it slowly. A study in Portland, Oregon, found that green roofs can retain up to 60% of the rainfall during a typical storm. But there's a catch. The effectiveness depends on the depth of the soil and the type of plants. For example, sedum, a type of succulent, is popular because it's drought-tolerant, but it's not as effective at water retention as native grasses with deeper roots. So, while green roofs are not a complete solution, they can significantly reduce the burden on urban drainage systems, especially when combined with other measures like rain gardens and permeable pavement.
❓ Question What is the main point the professor makes about green roofs?
A. A) They are the only solution to urban flooding.
B. B) They can help reduce flooding but have limitations.
C. C) They are most effective with shallow soil and sedum plants.
D. D) They are too expensive for most cities to implement.
✅ Correct Answer
B) They can help reduce flooding but have limitations.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word