We are always attracted by the sea. From it we can get food, minerals and treasures. For thousands of years, we just sailed on it but couldn't go far under its surface. We want to explore deep into the sea. However, we are not fish. We must breathe, so we can't stay underwater for long. To explore deep water, we face even more dangers and problems. A diver trying to stay underwater for a long time must breathe air or a special mixture of gases. He can wear a diving suit and have air pumped to him from above. He can carry a tank of air on his back and breathe through a special pipe. Water weighs 800 times as much as air. Tons of water pushes against a diver deep in the sea, so his body is under great pressure. When a diver is under great pressure, his blood takes in some of the gases he breathes. As he rises to the surface, the water pressure becomes less. If the diver rises too quickly, the gases in his blood form bubbles . The diver is then suffering from a kind of illness. This kind of illness can cause a diver great pains and even kill him. Why does a diver get a kind of illness?
Because he tries to do exercise underwater. Because he can't breathe enough air. Because he comes to the surface too quickly Because the air in his blood can be used up