How do animals communicate (交流) with each other? They have special “languages”. In fact, they are using signals (信号). Different signals have different meanings.

    For example, when a bee (蜜蜂) finds food somewhere, it flies home quickly. It can't speak, but it can tell others by dancing. Other bees will know where and how far the food is.

    Some animals show their feelings by making sounds. For example, when a dog is angry, it barks (吠). At this time, you'd better stay away from it. Birds can make several sounds to show different meanings. Sometimes we humans show feelings by making sounds instead of by speaking. For example, when we feel painful (疼痛的), we cry“Oh!”or“Ouch!”.

    We humans have languages and words. We can communicate face to face by speaking. We can write down what happened in order to remember clearly. We can also send (寄) messages to people far away. But animals can't.

根据短文内容，判断正误。

    If your pen broke at school today, what would you do? You would go to a shop and buy a new one. What if you could simply print out a real, working pen with your 3-D printer without leaving your room?

    Ten years ago people could only see 3-D printing in science fiction movies. But now 3-D printing is here and it's bringing big changes.

    Unlike normal printing that can only copy a 2-D picture with ink. 3-D printing can build almost anything made from material. The printer layers(分层) the material in different shapes to create the object you want to be copied.

    The 3-D printer has been used to make many different things. People have made cups, cars and even an airplane with it. Doctors have been using 3-D printers for several years. People's nervous systems(系统) have been printed out in 3-D form in medical research. Some body parts have been printed and used in hospital. Several months ago, doctors used a 3-D printer to rebuild the face of a person who had a bad accident. In the future, it is expected that the printer will make human organs(器官)to save more lives.

    However there are drawbacks to the printer. At the moment, printing can be quite slow and it's still rather expensive. The average(平均的) price of a household printer is around $1,700, not including the cost of the materials.

    But as the technology develops, it shouldn't be long before disadvantages are improved. Only time will tell where this new technology will take us.

Why salmon will newer get lost

    When you're packing for an adventure, what's the most important thing you'll need? If you don't want to get lost, you' need a map. Or better yet, a GPS. What about other animals? How do they know where they're going?

    While humans depend on technology to travel, some animals have something far more advanced. Researchers, mainly from Oregon State University, US, found that Chinook salmon have a "built in GPS" of the Earth's magnetic field(磁场). This means as soon as they are born they are able to direct themselves in the ocean. It acts like a big map inside their brain.

    Scientists placed some baby salmon into a big swimming pool. To simulate the Earth's magnetic field, they put magnetic coils(线圈) all around the pool. Then, by changing the direction of the coils, the salmon began to change their own direction. They started to face in the direction of their ocean feeding area. This is a safe place in the ocean where salmon can find food to eat. When the scientists changed the coils to the opposite side, the salmon also turned in the opposite direction. Just by using their "built-in GPS", the salmon were able to figure out the direction of their feeding area.

    How did Chinook salmon get their "built in GPS"? The scientists believe that their navigation(导航) skills came through evolution(进化). The fish that were able to reach the feeding area lived longer. Then they could pass on their navigation skills to their babies. So if you're ever lost and in need of some help, maybe you should ask a salmon to point you in the right direction!

    On a rainy day, about 150 volunteers worked for eight hours to clean up Carson Creek that is near a river. About nine tons of trash(H l)was taken out from there.

    "We did a good job, "said Alan Specter, the organizer of the event, "Were planning to come back here one more time, three years from now, Of course, we hope that there won't be so much trash next time."

    The trash came in all shapes, sizes, and colors: bottles, bicycles, batteries, furniture, clothing, plastic bags, dolls, and even a golf bag with a full set of golf clubs(球杆).

    The dirty and tiring work was done by two volunteer groups Save the Bay and Watch the Whales. Most of the volunteers came from a local police station and a fire station. And some of them were old people who had already retired (退休)。

    That day, it rained a little. All of them wore boots, gloves and raincoats. The work took place along a two- mile river with over 500 big yellow trash bags every where.

    No one found anything that cost much. A five- year-old boy found an earring which he thought might be worth a million dollars. He said he'd sell it. Then he'd donate half of the money to Watch the Whales, and use the other half to buy his favorite ice- cream every day.

    Many people laughed at the boy's story. However, it was easily found that the environment there did become better.