Listen to part of a lecture in an environmental science class. The professor is discussing the role of beavers in ecosystems.
Professor: Today we're going to talk about beavers, often considered a keystone species. Now, a keystone species is one that has a disproportionately large effect on its environment relative to its abundance. Beavers are a classic example. By building dams, they create ponds, which slow the flow of water and allow sediment to settle. This can reduce erosion downstream and improve water quality. But that's not all. The ponds they create become habitats for fish, amphibians, and waterfowl. And when beavers abandon a dam, the pond eventually drains, leaving behind a fertile meadow. These meadows are temporary but highly productive, supporting a variety of plant and animal life. So, even though beavers can cause localized flooding that may conflict with human land use, their overall impact on biodiversity is incredibly positive. Some scientists even call them 'ecosystem engineers.' But their role was not always appreciated; in the past, they were hunted extensively for their fur, and many populations disappeared. Today, reintroduction efforts are underway in many areas, and we're seeing the benefits.
❓ Pregunta What is the main point the professor makes about beavers?
A. They are a keystone species whose dam-building activities greatly benefit biodiversity.
B. They cause too much flooding and are therefore a nuisance to humans.
C. Their fur was the main reason they were hunted to extinction.
D. They only benefit their environment while they are actively building dams.
✅ Respuesta correcta
They are a keystone species whose dam-building activities greatly benefit biodiversity.
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