题目内容：

Many of us have wondered what Earth is like beneath the surface. So have writers and scientists. In French novelist Jules Verne’s masterpiece Journey to the Center of the Earth, explorers go down to Earth’s center and discover amazing wonders.

But in real life, human beings haven’t even come close to the planet’s core (核心). The core is over 6,000 km down. The deepest hole ever created, according to the BBC, is the Kola Superdeep Borehole in Russia, which only goes 12.3 km down.

So how do we know about everything down below without any samples？

One good way to start is to think about the Earth’s density (密度), Simon Redfern of the University of Cambridge in the UK told the BBC.

“The density of the material on Earth’s surface is much lower than the average density of the whole Earth, so that tells us there’s something that has greater density,” Redfern said.

The challenge is to find out which heavy materials the core is made of. And the main material scientists have found is iron. The idea is that when Earth formed 4.5 billion years ago, a lot of iron made its way down to the core, taking up about 80 percent of it. Today scientists are still working on finding out which other materials the core could be made up of.

You might also wonder how we know the size of the core. There’s a one-word answer: seismology (地震学).

When an earthquake happens, seismic stations around the world record the shockwaves it sends throughout the planet. It’s like hitting one side of the planet with a huge hammer and listening on the other side for the noise.

Early research found that some shockwaves, called “S-waves”, went missing. S-waves can only travel through solid material, but not through liquid, so they must have found something molten in Earth’s center. By following the S-waves’ paths, scientists found out that rocks became liquid around 3,000 km down.

There are still many questions about the Earth’s core to answer. But the study of the dark world below isn’t just for scientists’ curiosity.

The movement of Earth’s molten iron core builds up a powerful magnetic (有磁力的) field. It protects us from radiation from the sun and is needed for compasses and GPS systems to work.

So perhaps none of us will ever set eyes on the core, but it’s good to know it’s there.

1.The author mentions Jules Verne’s novel Journey to the Center of the Earth in the first paragraph to             .

A. discuss the possibility of going down to Earth’s center

B. show how much humans have discovered about Earth

C. paint a picture in our imagination of the dark world below

D. show humans’ deep interest in Earth’s center

2.We can learn from the article that “S-waves”                   .

A. are often used to predict earthquakes

B. cannot travel through liquid material

C. are the most noticeable shockwaves produced by earthquakes

D. can travel most rapidly at 3,000 kilometers below Earth’s surface

3.We can infer from the last three paragraphs that                  .

A. research into Earth’s core has hardly made any progress in recent years

B. improvements in GPS systems could help people find out more about Earth

C. Earth’s core helps to protect humans from harm

D. scientists are likely to reach Earth’s center within dozens of years