底

例句：

1. 1. The boat sank to the bottom of the lake.
   船沉到了湖底。
2. 2. The foundation of the building is made of concrete.
   这栋建筑的基础是用混凝土做的。
3. 3. The bottom layer of the soil is rich in nutrients.
   土壤的底层富含养分。