base of trajectory

例句：

1. 1.The base of the pyramid is the foundation of the entire structure.
   金字塔的基座是整个结构的基础。
2. 2. The base of the mountain was covered in snow.
   山的底部覆盖着雪。
3. 3.The base of the table is smooth and flat.
   桌子的底部是光滑且平坦的。