Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we’re going to discuss a surprising factor in urban pollution: trees. You might think trees are always beneficial, but research shows that certain trees, especially those that emit volatile organic compounds, or VOCs, can contribute to ground-level ozone formation. Ozone is a major component of smog, and it forms when VOCs react with nitrogen oxides in the presence of sunlight. In cities with high traffic, nitrogen oxides are abundant. So, when we plant trees like oaks or poplars, which release lots of VOCs, we might inadvertently increase ozone levels, especially on hot, sunny days. However, this doesn’t mean we should stop planting trees. Trees also absorb pollutants and provide shade, which can lower temperatures and reduce energy use. The key is to choose tree species that emit fewer VOCs, and to plant them strategically away from high-traffic areas. So, urban planners need to balance the benefits of trees with their potential downfalls.
❓ Câu hỏi What is the main point the professor makes about trees in urban areas?
A. Trees always improve air quality by absorbing pollutants.
B. Some trees can worsen smog by emitting VOCs that react with nitrogen oxides.
C. Planting trees near highways is the most effective way to reduce ozone.
D. Urban planners should remove all VOC-emitting trees to lower pollution.
✅ Đáp án đúng
Some trees can worsen smog by emitting VOCs that react with nitrogen oxides.
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