大学英语：The star will explode when its density increases to some extent

　　1. 星体的密度增大到一定程度时就会发生爆炸。

　　答： The star will explode when its density increases to some extent.

　　2. 你能想象黑洞的引力有多大吗?

　　答： Can you imagine how strong the gravitational pull of a black hole is ?

　　3. 假如有人掉进黑洞，他会认为很快能到达黑洞的中心。

　　答：If a man fell into a black hole, he would think that he reached the center of it very quickly.

　　4. 早在17世纪天文学家便对超新星有过报道。

　　答： Supernovae were reported by astronomers as early as in the seventeenth century.

　　5. 他已尽了全力以达到自己的目标。

　　答： He has exerted all his strength to attain his goal.