Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a surprising but important factor in urban pollution: trees. Now, we often think of trees as beneficial, and they are, but they can also contribute to air quality problems. Specifically, certain species of trees release volatile organic compounds, or VOCs. These VOCs, when combined with nitrogen oxides from car exhaust and sunlight, form ground-level ozone, which is a major component of smog. So in cities with heavy traffic, planting a lot of these trees can actually increase ozone levels, especially on hot, sunny days. For example, in Los Angeles, researchers found that certain types of oak trees were significant contributors to ozone formation. However, this doesn't mean we should stop planting trees. Instead, city planners need to choose tree species that emit fewer VOCs, and place them strategically. Also, reducing car emissions remains the most effective way to tackle smog. So, the key is not to vilify trees, but to understand the complex interactions in urban ecosystems.
❓ 質問 What is the main point the professor makes about trees in urban areas?
A. Trees are always beneficial for air quality in cities.
B. Some trees can worsen smog by releasing chemicals that react with pollutants.
C. City planners should replace all trees with low-emission alternatives.
D. Reducing car emissions has no effect on ozone levels if trees are present.
✅ 正解
Some trees can worsen smog by releasing chemicals that react with pollutants.
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
