单选题
The Greatest Mystery of Whales
The whale is a warm-blooded, air-breathing animal, giving birth to its young alive, sucking them—and, like all mammals, originated on land. There are many
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of this. Its front flippers (鳍状肢), used for steering and stability, are traces of feet.
Immense strength is
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into the great body of the big whales, and in fact most of a whale"s body is one gigantic muscle. The blue whale"s pulling strength has been estimated
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400 horsepower. One specimen was reported to have towed (拖) a whaling vessel for seven hours at the
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of eight knot (节).
An angry whale will
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. A famous example of this was the fate of Whaler Essex,
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was sunk off the coast of South America early in the last century. More recently, steel ships have
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their plates buckled (使弯曲) in the same way. Sperm whales (抹香鲸) were known to seize the old-time whaleboats in their jaws and crush them.
The greatest
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of whales is their diving ability. The sperm whale dives to the bottom for his
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food, the octopus (章鱼). In that search he is known to go as far down as 3,200 feet, where the
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is 1,400 pounds to a square inch. Doing so he will
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underwater as long as one hour. Two special skills are involved in this storing up enough
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(all whales are air-breathed)and tolerating the great change in pressure. Just how he does it scientists have not
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. It is believed that some of the oxygen is stored in a special
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of blood vessels, rather than just held in the lungs. And it is believed that a special kind of oil in his head is some sort of a compensating mechanism that
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adjusts the internal pressure of his body. But since you can"t bring a live whale into the laboratory for study, no one knows just how these things work.