After being under water for about 15 minutes, before even half of their oxygen has been used up, one of the diving instructors becomes aware that the current is getting stronger.
氣瓶中的壓縮空氣消耗還不過半，下海不過十五分鐘，潛水導遊警覺海中伏流漸漸變大，是漲潮時候！