单选题

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 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.
A. Right
B. Wrong
C. Not mentioned

【正确答案】 A

【答案解析】[解析] 由第一段第二句话可知“A black hole in the universe is not a solid object，like a planet，but it is shaped like a sphere”(宇宙中的黑洞像行星一样是不稳固的对象，但它的形状像一个球体)，由此可以推断黑洞是宇宙中的一部分。

单选题 Black holes exist but are difficult to observe.
A. Right
B. Wrong
C. Not mentioned

单选题 The center of a black hole is empty.
A. Right
B. Wrong
C. Not mentioned

【正确答案】 B

【答案解析】[解析] 由第一段第三句话可知“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，在黑洞的中心空间里有一个单点，具有无限密度)，还有第一段倒数第二句话“The center of a black hole would not really be a hole at all，but an infinitely dense point”(在黑洞的中心，可能根本不是一个真正的黑洞，而是一个无限密度的点)，由以上这些信息均可判断出黑洞的中心不是空的，所以这句话的表述是错误的。