The Greatest Mystery of Whales
The whale is a mammal - 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 whales body is one gigantic muscle. The blue whales 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__ South America early in the last century. More recently， steel ships have had their plates buckled in the same way. Sperm whales were known to __7__ the old-time whaleboats in their jaws and crush them.
The greatest mystery of whales is their diving ability. The sperm whale __8__ the bottom for his favourite food， the octopus. __9__ 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 submerged as long as one hour. Two feats are involved in this ： storing up enough __11__ and withstanding the great change in pressure. Just __12__ he dose 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__ 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 cant bring a live whale into the laboratory for study， no one __15__ just how these things work.
EXERCISE：
1. A)Their B)His 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)off the coast of B)of the coast of C0away the coast of D)in the coast of
7. A)hit B)seize C)damage D)overturn
8. A)sink to B)rest on C)dive to D)hide on
9. A)In that search B)Because of this C)In spite of that D)In support of this
10. A)so B)such C)above D)the same
11. A)air B)oxygen C)energy D)heat
12. A)what B)where C)how D)when
13. A)it is believed B)he believes C)we believe D)it believes
14. A)because of B)due to C)since D)owing to
15. A)communicates B)knows C)hears D)develops
答案：D A C B C A B C A A B C A C B