阅读下面短文，掌握其大意，然后从各题所给的四个选项（A、B、C和D）中，选出最佳选项．

　　With their shiny, grey bodies, dolphins（海豚）appear to be large fish．____1____, they are really warm-blooded mammals. Although they can stay under the water for up to 15 minutes ____2____, the dolphins must come up to breathe air through a hole on top of their heads.

　　Dolphins are social animals. Many of them even ____3____ around humans. In addition to being playful; they are helpful to men. For example ____4____ 400 B.C. the Great poet Arion was saved from ___5____ by a dolphin. From then until now, dolphins have been helping swimmers, ____6__ in trouble. Swimmers, however ,are not ___7____ humans they help. In some parts of the world, they help men ____8____ fish.

　　Dolphins are very clever. Its brain is even larger than a human's. Therefore, some people think a dolphin ____9__ smarter than a man, but ____10___, brain size is not the only measure of cleverness. Besides, measuring dolphin's cleverness in other ways is not possible ___11____ men cannot talk with them. But we can almost ____12____ that dolphins can talk with each other. They make different ____13____ which seem to be at least a form of language. Up to now men ____14___ able to find out how dolphins are talking. So no one really knows what they are thinking. If we could talk with them, perhaps they could teach us to be ___15____ they seem to be.

　　　 Dolphins（海豚）are not fish, but warm-blooded animals. They live in groups, and speak to each other in their own language. In this, they are like other animals, such as bees and birds. But dolphins are very different from almost all land animals. Their brain is nearly the same size as our own, and they live a long time―at least twenty or thirty years. Like some animals, dolphins use sound to help them find their way around. They also make these sounds to talk to each other and to help them find food. We now know they do not use their ears to receive these sounds, but the lower part of the mouth, called the jaw.

　　　 Strangely, dolphins seem to like man, and for thousands of years there have been stories about the dolphin and its friendship with people.

　　　 There is a story about sailors in the 19th century. In a dangerous part of the sea off the coast of New Zealand, they learnt to look for a dolphin called Jack. From 1871 to 1903, Jack met every boat in the area and showed it the way. Then in 1903 a passenger on a boat called The Penguin shot and wounded Jack. He recovered and for nine years more continued to guide all ships through the area－except for The Penguin.

　　　 Today, some people continue to kill dolphins, but many countries of the world now protect them and in these places it is against the law to kill them.

65. Dolphins are different from many other animals in that they _____.

A. live in groups　 B. have large brains　 C. are warm-blooded D. have their own language

66. Which of the following does the dolphin use to help it find its way around?

A. Its nose.　　　 　　　　 B. Its ears.　　　 　　　　　　 C. Its mouth.　　　 　　　 D. Its eyes.

67. Why did the sailors off the coast of New Zealand look for Jack?

A. He was lonely and liked to be with people. B. They enjoyed playing with him.

C. He was seriously wounded. 　　　　　　　　　　　　　　 D. They wanted his help.

68. By telling the story of Jack, the writer wanted to show that _____.

A. dolphins are friendly and clever B. people are cruel to animals

C. Jack is different from other dolphins D. dolphins should be protected by law