A black hole is created when a large star burns out. Like our sun, stars are unbelievably hot furnaces（熔炉）that burn their own matter as fuel. When most of the fuel is used up, the star begins to die.
The death of a star is not a quiet event. First there is a huge explosion. As its outer layer is blasted off into space, the dying star shines as brightly as a billion suns.
After the explosion gravity pulls in what's left of the star. As the outside of the star sinks toward the center, the star gets smaller and smaller. The material the star is made of becomes tightly packed together. A star is so dense that a teaspoon of matter from it weighs billion of pounds.
The more the star shrinks, the stronger the gravity inside it becomes. Soon the star is very tiny, and the gravity pulling it in is un-believably strong. In fact, the gravity is so strong that it even pulls light into the star! Since all the light is pulled in, none can go out. The star becomes black when there is no light. Then a black hole is born!
That's what we know about black holes. What we don't know is this ： What happens inside a black hole after the star has been squeezed into a tiny ball? Does it keep getting smaller and smaller forever? Such a possibility is hard to imagine.
But if the black hole doesn't keep shrinking, what happens to it? Some scientists think black holes are like doorways to another world. They say that as the star disappears from our universe, it goes into another universe. In other words a black hole in our universe could turn into a " white hole" in a different universe. As the black hole swallows light, the white hole shines brightly-somewhere else. But where? A different place, perhaps, or a different time-many years in the past or future.
Could you travel through a black hole? Right now, no. Nothing we know of could go into a black hole without being crushed. So far the time being, black holes must remain a mystery.
Black holes are a mystery-but that hasn't stopped scientists from dreaming about them. One scientist suggested that in the future we might make use of the power of black holes. They would supply all of Earth's energy needs, with plenty to spare. Another scientist wondered if a black hole could some day be used to swallow earthly waste-a sort of huge waste disposal（处理）in the sky!
When the star begins to die __________.

A．there is no fuel left in it

B．its outer layer goes into space first

C．a huge explosion will happen

D．it doesn't give off light any longer

Which of the following doesn't help produce a black hole?

A．The gravity inside the star is very strong.

B．The light can't go out of the star.

C．The star becomes smaller and smaller

D．The dying star shines very brightly.

The black hole __________.

A．continues becoming smaller and smaller all the time

B．goes into another universe and becomes a white hole

C．can pull in everything we know of in the world

D．will appear at another place at a different time

The author mainly intended to tell us __________.

A．New Scientific Discovery ： Black Holes

B．How Black Holes Came Into Being

C．What Black Holes Are

D．Travel Through A Black Hole