第二单元
1.常考单词：
escape，explode，collapse，shrink，gravity，measurement，basis，launch，convincing，companion，speculation，swallow，operate，to make use of，a great many，above all
2. 常考句子：
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.