Listen to part of a lecture in an astronomy class. The professor is discussing the formation of planets.
Professor: So, we've talked about how stars form from collapsing clouds of gas and dust. But what about the planets that orbit them? Well, these planets don't just appear out of nowhere. They form from a rotating disk of material that surrounds the young star, called a protoplanetary disk. In this disk, small particles of dust and ice collide and stick together, gradually building up larger and larger bodies. These are called planetesimals. Over millions of years, these planetesimals can grow into full-sized planets through a process we call accretion. Now, an interesting question is why the inner planets, like Earth, are rocky, while the outer planets, like Jupiter, are mostly gas and ice. One key factor is temperature. In the inner part of the disk, it's too hot for volatile compounds like water and methane to condense into solid ice. So only rocky and metallic materials can solidify. In the colder outer regions, these volatiles can condense, allowing planetesimals to accrete much more material, which explains why the outer planets are so massive.
❓ 문제 According to the professor, what is the main reason that the inner planets are rocky while the outer planets are gas giants?
A. The inner planets formed earlier than the outer planets.
B. The temperature in the inner disk was too high for volatile compounds to condense.
C. The outer planets captured gas from the nearby star.
D. The inner disk had less dust and ice overall.
✅ 정답
The temperature in the inner disk was too high for volatile compounds to condense.
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
