in the sea 在海里
例句与用法:
Sealed containers of nuclear waste have been dumped in the sea.
盛有核废料的密封容器被丢在海里.
Swimming in the sea is great fun.
在海里游泳很好玩.
on the sea 在海（面）上
例句与用法:
The sun glared on the sea.
太阳在海上发出令人目眩的光芒.
at sea 离开陆地(茫然)
例句与用法:
He felt completely at sea in his new school.
他在新学校中感到茫然不知所措.
The refugees were at sea for forty days before reaching land.
这些难民在海上漂泊了40天后,他们的船才靠岸.