num buoy

例句：

1. 1. The boat was drifting with the current, and we needed a num buoy to keep it from getting lost.
   船随波逐流，我们需要一个浮标来防止它迷失方向。
2. 2. The sailors used num buoys to mark the boundaries of their fishing grounds.
   水手们使用浮标来标记他们的捕鱼区域的边界。
3. 3. The num buoy was a crucial part of the navigation system for the ship.
   这个浮标是船只导航系统的重要组成部分。