The sea has always interested man. From it he can get food, minerals, and treasure.    1   But he

could not go far beneath its surface.

          2   However, he is not a fish. He must breathe air, so he can't stay under the water's surface for

any length of time. To explore deep water, man faces even more dangers and problems.

     A diver who wants to stay under water for more than a few minutes must breathe air or a special

mixture of gases.   3   He can carry a tank of air on his back and breathe through a nose and a

mouthpiece. Water weighs 800 times as much as air. Tons of water pushes against a diver deep in the

sea.   4   

     When a diver is under great pressure, his blood takes in some of the gases he breathes. As he rises

to surface, the water pressure becomes less. If the diver rises too quickly, the gases in his blood form

bubbles(气泡). The diver is then suffering from the bends(潜水夫病). The bends can cause a diver to

double up in pain.     5   

A. His body is under great pressure.

B. Scientists are trying to find more about the sea.

C. For thousands of years, he could sail on it.

D. They can even kill him.

E. He can wear a diving suit and have air pumped to him from above.

F. The water pressure can cause a diver to breathe with difficulty.

G. Man wants to explore deep into the sea.