A、The pressure that people get. B、The cold and darkness. C、The greatest one is breathing. D、The beach is not clean. C细节辨认题 。问题是关

Everyone enjoys the seaside. Beaches are ideal places for games, sunbathing and swimming.  (29)A warm sun, a clean sea and a sandy shore are most people’s idea of the perfect holiday setting But Beyond these sunny, warm, shallow shorelines lie the cold depths of the sea. Here below the surface, where the sun’s rays and light quickly fade away, is a place as hostile to men as the black depths of space. Every 33 feet Below the surface the pressure on every inch of the human body increases by I atmosphere. (30)Down to 33 feet the body, s subjected to the same pressure we endure in the upper world without even noticing it--14.7 pounds to the square inch. At 600 feet down in the sea the pressure exerted by that great volume of water is over 280 pounds per square inch. The wonderful thing is that the human body can survive such pressure without ill effects. But pressure is not the only problem. There is also the cold and the dark ness. As you have just heard, the sun’s rays only reach a short way down into the sea. The water temperature falls and the light dints to complete blackness as you go lower down.
     The sea is not an empty space--it is full of life, some forms of which are dangerous to men. (31) Of course the east problem of all is breathing. Every breath of air you take must be pumped to you from above or carried with you in tanks.  You must be extremely careful when you come up again from the depths in order to avoid the painful and often deadly disease known as "the bends". When a diver only breathes compressed air, nitrogen builds up in his blood stream.