mark buoy

例句：

1. 1. The ship's crew marked the spot with a large red flag.
   船上的船员用一个大红旗在那个地点做了标记。
2. 2. The buoy was used to guide ships through the fog.
   这个浮标用来引导船只穿过雾。
3. 3.The buoy was a crucial part of the navigation system.
   这个浮标是导航系统的关键部分。