F This is particularly true in health care, a market in which scarce（稀罕的）goods are ridiculously expensive, but needed by everybody.

　　第6部分：完形填空（第51～65题，每题l分，共15分）

　　下面的短文有l5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）- 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. （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 reposed 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 jaws

　　and crush them

　　The greatest mystery of whales is their diving ability. The sperm whale can （58）the bosom 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 l,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