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.
The sea is very deep in some places. There is one spot, near Japan, where the sea is nearly 11 kilometres deep. The highest mountain in the world is about 9 kilometres high. If that mountain were put into the sea at that place, there would be 2 kilometres of water above it.
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, swimmes cannot sink! Fish cannot live in the Dead Sea.
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 them.
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.
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.
The deeper divers goes down in the sea, ____.（ ）
事实细节题。由文章第五段最后一句话可知，潜水者越深入海底，他们会发现海水变得越冷。
