Unit 2 习题：
escape, explode, collapse, shrink, gravity, measurement, basis, launch, convincing, companion,
speculation, swallow, operate, to make use of, a great many, above all
1) ~6) 与常考句型相同。
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.