题目内容：
根据下列文章,请回答题。The Greatest Mystery Of WhalesThe 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 __________(1) of this. Its front flippers (鳍状肢), used for steering and stability, are traces of feet.Immense strength is__________2) 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 __________ (3) 400 horsepower. One specimen was reported to have towed (拖) a whaling vessel for seven hours at the__________ (4) of eight knots (节).
An angry whale will __________ (5) a ship.
A famous example of this was the fate of whaler Essex (6) was sunk off the coast of South America early in the last century. More recently, steel ships have__________ (7) 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 __________ (8) of whales is their diving ability. The sperm whale dives to the bottom for his __________ (9) food, the octopus (章鱼). In that search he is known to go as far down as 3,200 feet, where the __________ (10) is 1,400 pounds, to a square inch. 13oing so he will __________ (11) underwater long as one hour. Two special skills are involved in this: storing up enough __________ (12) (all whales are air-breathed) and tolerating the great change in pressure. Just how he does it scientists have not__________ (13). It is. believed that some of the oxygen is stored in a special __________ (14) 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 compensating mechanism that __________ (15) 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. A．aspects
B．signs
C．ways
D．reasons
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