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(球體)。 Astronomers(天文學家) think that at the center of a black hole there is a single point in space with infinite(無限的) density(稠密)。 This single point is called a singularity(奇點)。 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(視界) only 18 miles across.
The nearest black holes would be dozens of light years away from Earth. One light year is about 6 trillion(萬億) 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
參考答案：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指明本題答案。本題中space 不是空間，而是宇宙、太空的意思 ，跟課文中universe同義。
2 A 答案在第二段第一句話裡：Although black holes do exist， they are difficult to observe。
3 B 這個陳述是錯誤的。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。天文學家認為黑洞中心有個密度無限大的點，所以黑洞並不是空的。
4 C 關於gravity(重力)是怎麼形成的，文章中沒有提到。
5 C 這個問題——太陽是宇宙中最重的'星球——文章中也沒有提到。
6 B 第二段給出的第三個原因the nearest black holes would be dozens of light years away from Earth表明離我們最近的黑洞有dozens of(許多，好幾打)而不是hundreds of(成百上千的)光年，所以本題描述錯誤。
7 A 最後一段第一句告訴我們Hubble Space Telescope provided evidence that black holes exist哈勃望遠鏡提供了黑洞存在的證據，正是通過這種方式，哈勃望遠鏡幫助科學家們更好地瞭解了宇宙的本質。因此該陳述正確。
