Unit 2 练习：
escape， explode， collapse， shrink， gravity， measurement， basis， launch， convincing， companion，
speculation， swallow， operate， to make use of， a great many， above all
1） Astronomers and scientists think that a black hole is a region of space into which matter has fallen and from which nothing can escape.
2） The theory is that some stars explode when their density increases to a particular point.
3） Some people think that the Start of Bethlehem could have been a supernova.
4） If a man fell into a black hole， he would think that he reached the center of it very quickly.
5） It is only recently that astronomers have begun specific research into black holes.
6） On the other hand， scientists have suggested that every advanced technology could one day make use of the energy of black holes for mankind.
7） There might be a massive black hole at the center of our galaxy swallowing up stars at a very rapid rate.
8） They show us a world which operates in a totally different way from our own and they question our most basic experience of space and time.
Astronomers have not yet fully solved the problem of what a black hole is.
It is said that black holes are able to swallow up all the objects around them， such as stars .
The research of black holes is just beginning and speculation about them are endless.
Scientists still can not tell what happens inside a black hole.
It is still impossible for scientists to tell what happens inside a black hole.
If we understood black holes， they would not be so fearful .
Black holes will not be so fearful if we get to know them.
1.Astronomers and scientists think that a black hole is a region of space ______ which matter has fallen and ______ which nothing can escape.
A.towards … towards B.into … from C.out of … from D.through… from
答案是B.考点：定语从句中介词+which 的结构；fall into 掉进去； escape from 从… 逃离。
答案：It is impossible to say what happens inside the black hole.
答案：It is only recently that astronomers have begun specific research into black holes.
答案：Some stars explode when their density increases to a certain point .
Unit 2 单元课后练习
Ⅰ Word Spelling
1.密度 n.d _ _ _ _ _ _ _ _
2.（使）倒塌，（使）崩溃 v.c _ _ _ _ _ _ _ _