完形填空 .   
    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     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 knot (节).
    An angry whale will     5    . 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. Doing so he will     11    underwater as 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 a 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.1.