VOA慢速英语:Blue Holes: Some of the Least Explored Areas on Earth

open up打开

例句：In some places there was no way through for the railway line, so new passages had to be opened up with explosives.
      有些地方无法铺设铁路线, 因此一些新的路段得用炸药炸开。

2.Yet these areas are filled with life forms that have adapted to the extreme conditions.

adapt to变得习惯于…, 使适应于, 能应付…

例句：I adapted quickly to the new climate.
      我很快地适应了这种新的气候。

      The professor adapted his lecture to his audience.
      教授使他讲的课适合于听众。

3.This layer acts like a cap on top of the layered mixture, and keeps out oxygen from the atmosphere.

on top of在…上边, 在…上方

例句：Put this book on top of the others.
       把这本书放在其他书的上边。