单选题

The Sea

What do you know about the sea? We know that it looks very pretty when the sun is shining on it. We also know that it can be very rough when there is a strong wind. What other things do we know about it?
The first thing to remember is that the sea is very big. When you look at the map of the world you will find there is more water than land. The sea covers three quarters of the world.
The sea is also very deep in some places. It is not deep everywhere. Some parts of the sea are very shallow. But in some places the depth of the sea is very great. 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! What a deep place!
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 saltier than other parts. There is one sea, called the Dead Sea, which is very salty. It is so salty that swimmers 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 so small that it is hard to see them. Many fish live by eating these.
The sea can be very cold. Divers who go 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. But he cannot go very deep. Some people who wanted to go very deep used a very strong diving ship! They went down to the deepest part of the sea in it. They went down to a depth of eleven kilometers!