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__

　　参考答案：

　　1 将as 改为since或者because。在表示原因的连接词中，只有as引导的原因状语从句不能位于主句之后，只能位于句首。
　　2 将adequate 改为inadequate，或者在are后加not。从逻辑上分析，因为我们拥有的科学术语“不充足”，所以才无法回答这个问题，所以用否定形式。
　　3 在which 前加into。这是一个定语从句，意思是“黑洞是太空中物质可以掉进去的地方”，所以定语从句应该为“into which matter has fallen”。
　　4 将but 改为 so。 上文已提到“连光都无法从黑洞中逃出”，所以我们根本无法看到黑洞。这里应该是因果关系，而不是转折关系。
　　5 将thus改为so。这句话的意思是“那只是空间—或者我们认为它只是空间”。so做 think 的宾语，thus 只能做连词，不能做宾语。
　　6 将which 改为whose。这个定语从句的意思是“它是一颗星，其密度非常大，由于自身的引力，它在不断地收缩”。matter 属于star，所以关系代词应该用whose。
　　7 去掉in。result为不及物动词，意为“形成了”，而“result in sth。”意为“导致某结果”。
　　8 将masses 改为mass。mass 可指“大量的物质”，而“the masses”特指“劳动群众”，用在此处不妥。
　　9 将ideas 改为idea。“idea”在表达“印象”时，为不可数名词，不可以用复数。

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