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 is just a roof, but in cities, where concrete and asphalt cover most surfaces, rainwater has nowhere to go. It rushes into storm drains, which can overflow, causing floods. Green roofs, covered with plants and soil, absorb rainwater like a sponge. A study in Portland, Oregon, found that a typical green roof can retain up to 60 percent of annual rainfall. 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-resistant, but it absorbs less water than native prairie plants. Also, green roofs provide insulation, reducing energy costs by up to 25 percent. However, the initial installation cost is high, which discourages some building owners. Despite this, many cities now offer tax incentives to promote green roofs. So, while they're not a one-size-fits-all solution, they're a key tool in managing urban water.
❓ Вопрос What is the main point the professor makes about green roofs?
A. They are too expensive and not worth the investment.
B. They help reduce flooding by absorbing rainwater, but their effectiveness varies.
C. They are only useful in dry climates.
D. They eliminate the need for storm drains in cities.
✅ Правильный ответ
They help reduce flooding by absorbing rainwater, but their effectiveness varies.
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