Why don't birds get lost on their long flights (飞行) from one place to another? Scientists have studied this puzzle for a long time. Now they're starting to fill in the blanks(空白).

    Not long ago, experiments showed that birds use the sun to guide them during daylight hours. How do birds fly at night? Tests with artificial stars, which are made by people, have proved that certain night-flying birds are able to follow the stars in their long-distance flights.

    They found a bird that spent its lifetime in a cage and never flew under a natural sky. But it was born with the ability to use the stars to look for the direction. This bird's cage was placed under the sky filled with artificial stars. Any change in the position of the artificial stars caused a change in the direction of the bird's flight. From the experiment, they found that the bird tried to fly in the same direction as those artificial stars moving under the natural sky.

    But the stars are of course birds' main ways of navigation (航行), when the stars are hidden by clouds, they can still find their way by such landmarks (路标) as river courses, mountain ranges (山脉), coast lines and so on. Because of this ability, people use the dove (鸽子) to send messages in some fields. For example, the doves were used to send messages in both World War I and World War II. During that time, thousands of doves were used to carry important messages in order to save the lives of many thousands of people. So it is also the symbol of peace.

    But when it's too dark to see these things, the doves are not able to find their way. They only circle helplessly and get lost.

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    Have you ever stood beside the ocean and stared at the waves (波浪)? The way they move is changing! Nothing is more peaceful than watching the movement of water.

    Every ocean has waves. Unless you are lucky enough to live by the sea, though, you probably can't watch the waves very often. How would you like to have your own wave machine? Making one is easy and a lot of fun.

    Now that you have made your ocean, put your bottle on its side. Wait a minute. The water win be on the bottom. The oil and paint thinner mixture will be on the top. Now tip (倾斜) the bottle back and forth (反复来回) and watch the waves.

    The World Health Organization(世界卫生组织) says air pollution kills seven million people around the world each year. Even if polluted air does not kill us, it can make us very sick.

    However, breathing dirty air may do more than hurt your body. It can also affect(影响) your brain and your ability to think.

A new study shows that air pollution can cause a "huge" reduction(减少)in our intelligence(智商).The researchers reported that long-term exposure(暴露) to air pollution can affect a person's mental(智力的) abilities in two areas: language and math.

Xi Chen, the researcher of the Yale School of Public Health led the study. He and his team found that breathing polluted air can reduce a person's education level by about one year.

    Chen said that the effect(结果) generally is worse for those over 64 years of age, for men and for those with little or no education.

    "The older persons-they are more affected. And we find, quite interestingly, men are more affected than women. And people working outdoors are more affected than people working indoors.

The researchers noted that the effect of pollution on language ability is even more serious as people age, especially among men and the less educated.

    Why were language skills more affected than math? There are two main kinds of tissue(组织)in the brain: white matter and grey matter. White matter is more connected with a person's language skills, while grey matter is connected to our ability to solve math problems. Studies have shown that air pollution has a great effect on the white matter in the brain, but not the grey matter.

    Chen said that air pollution did affect the math skills, just not as much as their language skills.

    A British company has made a new product to help us save money. The product is a wristband that gives us an electric shock if we spend too much money. The wristband is called Pavlok. It is linked to our bank account. It knows how much money we have in the bank. If we go shopping and there is not enough money in our bank account, the wristband makes an electric shock on our wrists. This warns us not to overspend. The company is called Intelligent Environments. It wants to work with banks to help customers with their money. So far, no banks in Britain have said they would ask their customers to wear Pavlok. They could start doing this in the future.

    The Pavlok wristband is part of the Internet of Things. This is the idea that everything in our life will be connected to the Internet. The CEO of Intelligent Environments, David Webber, said people liked the idea of the Pavlok. Shoppers would rather get a small electric shock in the store from the wristband than get a big shock later when they see their bank account. Mr. Webber said the Pavlok would be great for people who cannot stop spending because they have no power or their power is weak. He added that many young people have the "ostrich effect". This is when people put their heads in the sand and buy things rather than look at how much money they have in their bank accounts.

Welcome to our city—Nanning. It is a beautiful city with many trees and flowers. So it is called "Green City". There are many nice places to visit. Come and enjoy your trip to Nanning.

Health problems which are related to climate change are getting worse, say two research reports.

The report s followed 44 health problems that are related to climate change around the world. They include heat deaths, infectious diseases（传染病）and hunger. "All of them are getting worse," said Marina Remanello. She is research director of the Lancet Countdown project. "With global worming getting worse, doing nothing on climate and health will cost more than acting now, one of the reports says.

The reports are called "code red for a healthy future". One report is centred（集中）on the US and the other is centred on the whole world. The reports found some dangerous facts. At-risk populations like older people and the very young are more easily influenced by high temperatures. For people over 65, the researchers found they stayed living in warm places where it is easier for some diseases to spread. For example, coast areas are warm enough for dangerous bacteria （细菌）to grow. In some poor nations me season for disease-spreading mosquitoes（蚊子）has got longer since the 1950s.

The research also found that 72 percent of countries saw an increase in wildfires. And in 2020, up to 10 percent of the world's land surface was influenced by extreme（极端的）drought. In the US, the heat. fire and drought caused the biggest problems. The Pacific Northwest and Canada saw extreme neatwaves. An earlier study found that the heatwaves would not have happened if there were no human-caused climate change.