covering lemma

例句：

1. 1. The tree's trunk is covered in moss.
   这棵树的树干上长满了苔藓。
2. 2. The new paint covers the old stains on the wall.
   新的油漆覆盖了墙上旧的污渍。
3. 3. The scientist used acovering layer to protect the sample.
   科学家用一层保护层来保护样本。