outer guide

例句：

1. 1. The outerguide of the ship is a crucial partof navigation.
   船的外部指南是导航的关键部分。
2. 2. The outer limit of the parkis marked by a large sign.
   公园的外部界限被一个大标志标记。
3. 3. The outerlimit of the ocean is determined by thedepth of the water.
   海洋的外部界限由水的深度决定。