Listen to part of a lecture in an environmental science class. Professor: Today we're discussing the concept of 'urban heat islands,' a phenomenon where cities are significantly warmer than surrounding rural areas. This occurs because materials like concrete and asphalt absorb and re-emit heat more than natural landscapes do. Additionally, waste heat from vehicles and buildings adds to the effect. One surprising factor is the lack of vegetation, which normally cools the air through evapotranspiration. Now, some cities are implementing 'green roofs'—covering building tops with plants—to combat this. Studies show that green roofs can reduce surface temperatures by up to 30 degrees Celsius in summer. However, their effectiveness depends on the climate. In dry regions, they require significant irrigation, which can strain water resources. In contrast, in humid areas, they may not cool as efficiently due to high moisture in the air. So, while green roofs are promising, they're not a one-size-fits-all solution. What's the key takeaway?
❓ 题目 What is the professor's main point about green roofs?
A. They are the most effective solution for all urban heat islands.
B. Their cooling benefits vary depending on local climate conditions.
C. They are too expensive to implement on a large scale.
D. They work best in dry regions because of low water needs.
✅ 正确答案
Their cooling benefits vary depending on local climate conditions.
