rock-bottom

例句：

1. 1.The car's rock-bottom speed is 100 miles per hour.
   这辆车的最低速度是每小时100英里。
2. 2. The boat sank to its rock-bottom at the bottom of the lake.
   船沉到了湖底的最低点。
3. 3.The scientist found the rock-bottom of the ocean to be incredibly deep.
   科学家发现海洋的底部非常深。