Narrator: Listen to part of a lecture in an environmental science class.
Professor: Today we're going to talk about a fascinating example of ecological restoration: the reintroduction of wolves to Yellowstone National Park in the 1990s. As you know, wolves were hunted to extinction in the park by the 1920s. Without wolves, the elk population exploded. Elk overgrazed the willows and aspens along rivers, which led to erosion and a decline in beaver populations. In 1995, scientists reintroduced 14 wolves from Canada. The effects were dramatic. The wolves not only reduced elk numbers, but also changed their behavior. Elk started avoiding open river valleys, so vegetation began to recover. With more trees and shrubs, beavers returned, creating habitats for fish and birds. Even the rivers' physical structure changed, as stabilized banks reduced erosion. This is often called a 'trophic cascade'—a top predator's influence rippling down through the food web. It shows how interconnected ecosystems truly are.
❓ Вопрос What is the main point the professor makes about the reintroduction of wolves in Yellowstone?
A. A. It was controversial because wolves attacked livestock near the park.
B. B. It demonstrated that removing a top predator had caused widespread ecological damage.
C. C. It was successful only because elk were relocated to other areas.
D. D. It led to a decrease in beaver populations due to increased predation.
✅ Правильный ответ
B. It demonstrated that removing a top predator had caused widespread ecological damage.
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
