题目内容：

    Our home galaxy(星系), the Milky Way, makes for a pretty space picture, and it looks normal at a distance. But a new 3D map reveals a surprise:_______________________________.

The Milky Way is a spiral(漩涡型的) galaxy, in which stars and gas clouds exist mainly in its spiral “arms”. Our massive neighbor, the Andromeda galaxy(仙女座), is also spiral. Spiral galaxies usually appear very flat and easy to see through a telescope, said the researchers.

Using 1,339 large, pulsating(脉冲的) stars to make a 3D map of the Milky Way, researchers discovered instead that the galaxy’s disk of stars is increasingly twisting，most likely due to the spinning of the disk. And the farther the stars are from the center, the more twisted it becomes.

Previously, astronomers saw evidence of hydrogen clouds becoming warped(弯曲的)in the Milky Way This isn’t completely abnormal, because astronomers have noticed the same pattern of progressively twisting spirals in about a dozen other galaxies. But it does help them make more sense of our galaxy.

Because we live in this galaxy, that makes it harder to observe, and dust and starlight make it even more difficult when using telescopes. Trying to determine what our galactic center looks like is similar to trying to find the center of a forest you’re standing in.

“It is extremely difficult to determine distances from the Sun to parts of the Milky Way’s outer gas disk without having a clear idea of what that disk actually looks like,” lead study author Xiaodian Chen of the Chinese Academy of Sciences in Beijing said in a statement.

From afar, the Milky Way appears like a thin rotating(旋转的) disk of stars, orbiting the center every few hundred million years. In the center, hundreds of billions of stars and dark matter hold the galaxy together.

But as you move toward the outermost reaches of the galaxy, the gravitational glue of the center fades. In the outer disk, this keeps hydrogen gas from being restricted, which contributes to an S-shaped warping.

“Somewhat to our surprise, we found that in 3D our collection of 1339 stars and the Milky Way’s gas disk follow each other closely. This offers new insights into the formation of our home galaxy,” Richard de Grijs, senior study co-author and professor at Macquarie University’s Department of Physics and Astronomy, said in a statement. “Perhaps more importantly, in the Milky Way’s outer regions, we found that the S-like stellar(星的)disk is warped in a progressively Twisted spiral pattern.”

So the massive inner disk’s rotational force causes the outer disk to warp, the researchers concluded.

“This research provides a crucial updated map for studies of our galaxy’s stellar motions and the origins of the Milky Way,” said Licai Deng, co-author and senior researcher at the Chinese Academy of Sciences, in a statement.

1.Which of the following might be the missing sentence in the first paragraph?

A. The Milky Way is being warped and twisted by its stars.

B. The Milky Way is spiral and orbiting itself all the time.

C. The formation of our home galaxy is due to the force of gravity.

D. The origin of the Milky Way lies in its rotational force.

2.What does the underlined “this” refer to?

A. the Milky Way B. the gravitational glue

C. the fading of gravity D. the outermost reach of the galaxy

3.Which of the following is true according to the passage?

A. The galaxy we live in is unique for its special spirals.

B. The stars in the center of the Milky Way are more twisted.

C. The distance from the sun to other stars is already known to scientists.

D. The rotation of its inner center forces the Milky Way to twist.

4.What is the significance of this finding?

A. It reveals why the Milky Way is a flat and spiral galaxy.

B. It leads to a breakthrough of using 3D technology in space research.

C. It proves a previous way of observing the Milky Way while we are living in it.

D. It contributes to our knowledge about the Milky Way.