第6部分：完型填空(第51～65题，每题1分，共15分)
下面的短文有15处空白，请根据短文内容为每处空白确定1个最佳选项。
The Greatest Mystery of Whales
The whale is a mammal(哺乳动物)一warm—blooded，air-breathing，考试大giving birth to its young alive，sucking them—and，like all mammals，originated on land，There are many signs of this．________(51)front flippers(鳍肢)，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________ (52)has been estimated at 400 horsepower．One specimen was reported to have________ (53) a whaling vessel for seven hours at the________ (54)of eight knots．
An enraged whale will attack a ship．A.famous________ (55)of this was the fate of whaler Essex，which was sunk________(56)the coast of South America early in the last century．More recently ,steel ships have had their plates buckled(扭曲变形)in the same way．Sperm whales were known to________ (57)the old—time whaleboats in their jaw sand crush them．
The greatest mystery of whales is their diving ability．The sperm whale can________ (58)the bottom for his favorite food，the octopus(章鱼)．________ (59)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________ (60)he will remain submerged(水下的)as long as one hour．Two feats(绝技)are involved in this：storing up enough________ (61)(all whales are air-breathed)and withstanding the great change in pressure．Just________(62)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________ (63)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________ (64)you can’t bring a live whale into the laboratory for study，no one________(65)just how these things work.
51.A.Their B.It's C.Theirs D.Its
52.A.strength B.width C.height D.length
53.A.eaten B.crashed C.towed(拖)D.lifted
54.A.distance B.rate C.voyage D.sail
55.A.picture B.film C.example D.book
56.A.0ff B.of C.above D.over
57.A.hit B.seize C.damageD.kick
58.A.fly to B.jump on C.dive toD.crawl on
59.A.In B.On C.By D.At
60.A.SO B.such C.above D.the same
61.A.water B.oxygen C.energyD.heat
62.A.what B.who C.how D.which
63.A.it B.he C.she D.there
64.A.because of B.due to C.since D.owing to
65.A.communicatesB.knows C.hears D.develops
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