Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a surprising factor in climate change: the role of forests, but not just in absorbing carbon dioxide. Recent research has focused on how trees release volatile organic compounds, or VOCs. These compounds, like isoprene, are what give forests that fresh, piney scent. But when VOCs react with nitrogen oxides in the air—often from industrial pollution—they form aerosols, tiny particles that can either cool the Earth by reflecting sunlight or warm it by trapping heat, depending on their altitude and composition. Interestingly, in pristine forests, the natural VOCs actually help to clean the air by promoting the formation of certain low-level clouds, which shade the ground. However, in polluted regions, the same compounds can contribute to ground-level ozone and smog, worsening air quality. This dual role makes forests a complex piece in the climate puzzle, and scientists are now using satellite data to track VOC emissions globally. So, while planting trees is vital, we must also consider the chemical interactions that affect our atmosphere.
❓ คำถาม What is the main point the professor makes about volatile organic compounds released by trees?
A. They only help cool the Earth by forming clouds.
B. They always contribute to air pollution and smog.
C. Their effect on climate and air quality depends on environmental conditions.
D. They are more harmful than beneficial in all forest regions.
✅ คำตอบที่ถูกต้อง
Their effect on climate and air quality depends on environmental conditions.
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