外种皮

例句：

1. 1. The tree's outer bark is thick and rough.
   这棵树的外皮又厚又粗糙。
2. 2. The bird's feathers provide insulation and protection from the weather.
   鸟的羽毛提供了保温和抵御天气的保护。
3. 3. The crab has a hard outer shell to protect its soft body.
   螃蟹有坚硬的外壳来保护它柔软的身体。