改错：What is a black hole？ Well, it is difficult to answer the question

What is a black hole？ Well, it is difficult to answer the question,

as the terms we would normally use to describe a scientific phenomenon __1__are adequate here. Astronomers and scientists think that a black hole is __2__a region of space which matter has fallen and from which nothing can __3__

escape—not even light. But we can’t see a black hole. A black hole __4__exerts a strong gravitational pull and yet it has no matter. It is only space—or thus we think. How can this happen？ __5__

The theory is that some stars explode when their density increases to a particular point; they “collapse” and sometimes a supernova occurs.

The collapse of a star may produce a “White Dwarf” of a “neutronstar”—

a star which matter is so dense that if continually shrinks by the force of __6___its own gravity. But if the star is very large, this process of shrinking may be so intense that a black hole results in. Imagine the earth reduced to the __7__size of a marble, but still having the same masses and a stronger __8__gravitational pull, and you have some ideas of the force of a black hole. __9__And no matter near the black hole is sucked in. __10__