Black holes
Most scientists agree that black holes exist but are nearly impossible to locate. A black hole in the universe is not a solid object，like a planet ，but it is shaped like a sphere(球体)。 Astronomers(天文学家) think that at the center of a black hole there is a single point in space with infinite(无限的) density(稠密)。 This single point is called a singularity(奇点)。 If the singularity theory is correct ，it means that when a massive star collapses，all the material in it disappears into the singularity. The center of a black hole would not really be a hole at all， but an infinitely dense point. Anything that crosses the black hole is pulled in by its great gravity.
Although black holes do exist， they are difficult to observe. These are the reasons.
No light or anything else comes out of back holes. As a result，they are invisible to a telescope.
In astronomical terms， black holes are truly tiny. For example， a black hole formed by the collapse of a giant star would have an event horizon(视界) only 18 miles across.
The nearest black holes would be dozens of light years away from Earth. One light year is about 6 trillion(万亿) miles. Even the most powerful telescopes could not pick out an object so small at such a great distance.
In 1994 the Hubble Space Telescope provided evidence that black holes exist. There are still answers to be found， however， so black holes remain one of the mysteries of the mysteries of the universe.
1 Black holes are part of space.
A Right
B Wrong
C No mentioned
2 Black holes exist but are difficult to observe.
A Right
B Wrong
C No mentioned
3 The center of a black holes is empty.
A Right
B Wrong
C No mentioned
4 The attraction of two large stars leads to gravity.
A Right
B Wrong
C No mentioned
5 The sun is the heaviest star in the universe.
A Right
B Wrong
C No men
ntioned
6 The nearest black holes are hundreds of light years away from us.
A Right
B Wrong
C No mentioned
7 The Hubble Space Telescope helps scientists to understand the nature of the universe.
A Right
B Wrong
C No mentioned
参考答案：A A B C C B A
答案解析：
1 A 第一段第二行首句a black hole in the universe指明本题答案。本题中space 不是空间，而是宇宙、太空的意思 ，跟课文中universe同义。
2 A 答案在第二段第一句话里：Although black holes do exist， they are difficult to observe。
3 B 这个陈述是错误的。第一段第三行的句子astronomers think that at the center of a black hole there is a single point in space with infinite density。天文学家认为黑洞中心有个密度无限大的点，所以黑洞并不是空的。
4 C 关于gravity(重力)是怎么形成的，文章中没有提到。
5 C 这个问题——太阳是宇宙中最重的'星球——文章中也没有提到。
6 B 第二段给出的第三个原因the nearest black holes would be dozens of light years away from Earth表明离我们最近的黑洞有dozens of(许多，好几打)而不是hundreds of(成百上千的)光年，所以本题描述错误。
7 A 最后一段第一句告诉我们Hubble Space Telescope provided evidence that black holes exist哈勃望远镜提供了黑洞存在的证据，正是通过这种方式，哈勃望远镜帮助科学家们更好地了解了宇宙的本质。因此该陈述正确。
书香门第
