阅读理解
A
Dolphins (海豚) are not fish but mammals (哺乳动物). They live in groups, and speak to each other in their own language. In this way they are like many other animals, like bees. But dolphins are very different from almost all land animals. Their brain (脑) is nearly the same size as humans', so they are the cleverest animals. And they live for 20 to 30 years.
But what does the dolphin look like? The dolphin has teeth, and eats fish. It can grow up to three and a half metres long. Its nose is very long. Like some other animals, the dolphin uses sound to find its way. They make sound to talk to each other and to help find food. We now know they don't use their ears to listen to the sound, but the jaws (颚).
Dolphins are friendly to people. They often save people in the sea. So many people like them.
，②×2﹣①，得y=