Listen to part of a lecture in an environmental science class. Professor: Today we're going to discuss a fascinating example of ecological restoration: the reintroduction of gray 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. The elk overgrazed the willow and aspen trees along riverbanks. This led to erosion and a decline in bird populations that depended on those trees. In 1995, scientists reintroduced 14 wolves from Canada. The effects were dramatic. The elk changed their behavior, avoiding areas where wolves were active. This allowed vegetation to recover. With trees growing again, beavers returned, and their dams created habitats for fish and amphibians. Even the rivers' paths became more stable. This process, known as a trophic cascade, shows how a top predator can shape an entire ecosystem. The park is now more balanced, though debates continue about wolf management in the region.
❓ Câu hỏi What was the main consequence of the elk population explosion in Yellowstone before the wolf reintroduction?
A. A) The elk migrated to other regions.
B. B) Overgrazing damaged riverbank vegetation.
C. C) Bird populations increased significantly.
D. D) The river paths became more stable.
✅ Đáp án đúng
B) Overgrazing damaged riverbank vegetation.
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