完形填空

　　阅读下面的短文，文中有15处空白，每处空白给出了4个选项，请根据短文的内容从4个选项中选择1个最佳答案。

The Greatest Mystery of Whales

　　The whale is a mammal一warm—blooded,air-breathing,giving birth to its young alive,sucking them—and,like all mammals,originated on land,There are many signs of this．____1____front flippers,used for steering and stability,are traces of feet.

　　Immense strength is built 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___2_____ has been estimated at 400 horsepower．One specimen was reported to have___3_____a whaling vessel for seven hours at the_____4___ of eight knots．

　　An enraged whale will attack a ship．A famous___5_____ of this was the fate of whaler Essex,which was sunk___6_____the coast of South America early in the last century．More recently ,steel ships have had their plates buckledin the same way．Sperm whales were known to____7____ the old—time whaleboats in their jaw sand crush them．

　　The greatest mystery of whales is their diving ability．The sperm whale can____8____ the bottom for his favorite food,the octopus．___9_____ that search he is known to go as far down as 3,200 feet,where the pressure is 1,400 pounds,to the square inch．Doing___10_____ he will remain submergedas long as one hour．Two featsare involved in this:storing up enough_____11___ and withstanding the great change in pressure．Just____12____he does it scientists have not determined．It is believed that some of the oxygen is stored in a special system of blood vessels,rather than just held in the lungs.And_____13___ is believed that a special kind of oil in his head is some sort of compensating mechanism that automatically adjusts the internal pressure of his body．But____14____ you can't bring a live whale into the laboratory for study,no one___15_____just how these things work.

　　1 A Their B It's C Theirs D Its

　　2 .A strength B width C height D length

　　3. A eaten B crashed C towed D lifted

　　4. A distance B rate C voyage D sail

　　5. A picture B film C example D book

　　6 .A 0ff B of C above D over

　　7. A hit B seize C damage D kick

　　8. A fly to B jump on C dive to D crawl on

　　9. A In B On C By D At

　　10 .A SO B such C above D the same

　　11. A water B oxygen C energy D heat

　　12 .A what B who C how D which

　　13 A it B he C she D there

　　14. A because of B due to C since D owing to

　　15 .A communicates B knows C hears D develops

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