概括段落大意和补全句子：阅读下面短文，请完成短文后的二项测试任务：(1)从第1~5题后所给的六个选项中为第①~⑤段每段选择一个正确的小标题；(2)从第6~10题后所给的六个选项中选择五个正确选项，分别完成每个句子。 

       The sea is very big. Look at a map of the world. There is less land than sea. The sea covers three quarters of the world. 
     ①The sea is very deep in some places. There is one spot, near Japan, where the sea is nearly 11 kilometers deep. The highest mountain in the world is about 9 kilometers high. If that mountain were put into the sea at that place, there would be 2 kilometers of water above it.  

     ② If you have swum in the sea, you know that it is salty. You can taste the salt. Rivers, which flow into the sea, carry salt from the land into the sea. Some parts of the sea are less salty than other parts. There is one sea, called the Dead Sea, which is very salty. Because it is very salty, swimmers cannot sink! Fish cannot live in the Dead Sea.  

     ③ In most parts of the sea, there are plenty of fishes and plants. Some live near the top of the sea. Others live deep down. There are also millions of tiny living things that float in the sea. These floating things are very small. It is hard to see them. Many fish live by eating these.  

     ④ The sea can be very cold. Divers, who dive deep down in the sea, know this. On the top the water may be warm. When the diver goes downwards, the sea becomes colder and colder.  

     ⑤ Another thing happens. When the diver goes deeper, the water above presses down on him. It squeezes him. Then the diver has to wear clothes made of metal.