Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a surprising solution to water pollution: constructed wetlands. Now, you might think of wetlands as natural ecosystems, but these are human-made systems designed to mimic the natural filtering processes of marshes and swamps. When wastewater, such as runoff from farms or factories, flows through a constructed wetland, plants and microorganisms work together to remove pollutants. The roots of cattails and reeds provide a surface for bacteria to attach and break down harmful nitrogen and phosphorus compounds. Additionally, the slow movement of water allows sediments to settle out, and sunlight helps kill some pathogens. The key advantage is cost-effectiveness—constructed wetlands require less energy and maintenance than traditional treatment plants. However, they do need a large area of land and take time to establish. So, while not suitable for every situation, they offer a sustainable option for rural communities. Now, let's consider a specific example...
❓ Câu hỏi What is the main advantage of constructed wetlands mentioned by the professor?
A. A. They require less land than traditional treatment plants.
B. B. They are more effective at removing heavy metals.
C. C. They are less expensive to operate than conventional systems.
D. D. They can be built quickly in any environment.
✅ Đáp án đúng
C. They are less expensive to operate than conventional systems.
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