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 (密度).
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 black holes. As a result, they are invisible to a telescope.
●In astronomical terms, black holes are truly. 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 universe.
单选题
Black holes are part of space.
【正确答案】
A
【答案解析】[解析] 题干大意：黑洞是太空的一部分。根据space回原文定位，文中首段第三句：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(密度). 故答案选A。
单选题
Black holes exist but are difficult to observe.
【正确答案】
A
【答案解析】[解析] 题干大意：黑洞是存在的，但是很难观察到。题干中的关键词为difficult，根据它回原文定位，在首句能找到difficult的近义词impossible。文章首句：Most scientists agree that black holes exist but are nearly impossible to locate. 黑洞确实存在，但很难定位。本句与题意信息相符，故答案选A。
单选题
The center of a black hole is empty.
【正确答案】
B
【答案解析】[解析] 题干大意：黑洞的中心是空的。根据中心词the center来定位，首段倒数第一句：at the center of a black hole there is a single point in space with infinite(无限的)density(密度). 由此可知其中心不是一个洞，证明中心不是空的，故答案选B。
单选题
The attraction of two large stars leads to gravity.
单选题
The nearest black holes are hundreds of light years away from us.
【正确答案】
B
【答案解析】[解析] 题干大意：离我们最近的黑洞也有几百光年。根据中心词nearest定位，原文倒数第二段提到：The nearest black holes would be dozens of light years away from Earth. 据此，离地球最近的黑洞有几十(dozens)光年远，而不是“hundreds”。故答案选B。
单选题
The Hubble Space Telescope helps scientists to understand the nature of the universe.
【正确答案】
A
【答案解析】[解析] 题干大意：哈勃太空望远镜帮助科学家了解宇宙的本质。根据专有名词the Hubble Space Telescope回原文定位，不难发现相关信息在最后一段。最后一段提到：In 1994 the Hubble Space Telescope provided evidence that black holes exist. 哈勃太空望远镜提供了黑洞存在的证据。这也就是说帮助科学家了解宇宙，原文信息与题干所述是一致的。故答案选A。