All oceans are seas, but not all seas are oceans.
All seas are bigger than lakes, but most are smaller than oceans.
每个 sea比湖大, 但是大多数的 sea比 ocean小.
There are only five oceans on Earth: the Atlantic Ocean, the Pacific, the Arctic, the Antarctic and the Indian Ocean.
上地球上只一有五个oceans: the Atlantic Ocean, the Pacific Ocean, the Arctic Ocean, the Antarctic Ocean and the Indian Ocean.
Collectively, these oceans and any sea that connects to them can be called 'the Ocean'.
每个在 ocean的水, 而且每个连接一个 ocean的sea,都是一个大 ocean. 它叫 'the ocean'.