VOA慢速英语:Keeping Plants and Trees Warm When Temperatures Drop

例句：The snow hardened until ice was formed.
       雪成冰后变硬了。

      His mind hardened as he became used to difficulty.
      他坚强起来了, 因为他已习惯于困难。

2.defense n.防卫,防卫物

3.moisture n.湿气,水分,降雨

例句：The desert air contains hardly any moisture.
      沙漠的空气几乎不含一点湿气。

4.absorb vt.吸收（液体、气体等）; 吸收（热、光、能等）

例句：Dry earth absorbs water quickly.
      干土吸水很快。

5.protective a.给予保护的,保护的

例句：We feel safe with a protective device in the house.
      我们因为家里有了防护装置而感到安全。

      A mother naturally feels protective towards her children.
      做母亲的天生要保护自己的孩子。

6.vegetation n.植物

例句：This place is desolate of all vegetation.
      这个地方不长草木。