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

例句：This is a reflection of their frailty.
      这是他们虚弱的反映。

2.vertical adj.垂直的, 竖的

例句：He climbed the vertical cliff.
      他攀登陡峭的悬崖。

      The northern side of the mountain is almost vertical.
      这座山的北坡几乎是垂直的。

3.atmosphere n.大气, 大气层,大气圈

例句：Changes in the climate are due to pollution of the atmosphere.
      由于对大气层的污染而造成了气候变化。

4.underneath prep.在…底下；隐藏（或掩盖）在下面

例句：The ball rolled underneath the table.
      球滚到了桌下。

      What have you got underneath your shirt?
      你的衬衫里面有什么?

5.ecosystem n.<生>生态系统

例句：There are highly sensitive and delicately balanced ecosystems in the forest.
      森林里有高度敏感、灵敏平衡的各种生态系统。

6.submarine n.潜艇

例句：The submarines surfaced.
      潜艇浮出了水面。