Narrator: Listen to part of a lecture in a geology class. Professor: So, we've been discussing how Earth's surface changes over time, and today I want to focus on a specific type of landform called a kettle lake. Now, kettle lakes form during glacial retreat. Picture a large glacier that's slowly melting and moving backward. As it retreats, chunks of ice can break off and become buried under sediment—sand, gravel, and rock that the glacier has pushed along. Over time, the surrounding sediment builds up around these ice blocks. When the ice eventually melts, it leaves behind a depression—a hole in the ground. This depression often fills with water from rainfall or melting snow, and voilà, you have a kettle lake. What's interesting is that these lakes are usually shallow and have no natural inlet or outlet, so their water levels depend entirely on precipitation and groundwater. This makes them sensitive to climate changes. Also, the sediment layers at the bottom of these lakes can preserve pollen and other organic material, which scientists study to reconstruct past climates. So, kettle lakes aren't just scenic; they're valuable archives of environmental history.
❓ Câu hỏi According to the professor, why are kettle lakes considered valuable to scientists?
A. They provide a source of fresh water for nearby communities.
B. Their bottom sediments can contain evidence of past climates.
C. They are formed by volcanic activity and help predict eruptions.
D. They are the only lakes that contain glacial ice year-round.
✅ Đáp án đúng
Their bottom sediments can contain evidence of past climates.
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
