All over the world the need for more laptops and computers increases each year. Networks have been part of our life. Probably everyone with a portable device （移动设备）has once logged on to a public WiFi network without paying for it, while they are having a coffee, on a train, in a shopping mall or at a hotel. However, is this kind of public WiFi network safe?

    Some networks are better protected than others because encryption （加密）methods are used. Therefore, they are safer than others. But a survey in 2015 showed that more than 950 million records were not protected, including addresses, emails, birth dates, phone numbers, passwords and so on. These open WiFi networks are really not safe, because it is very easy for hackers （黑客） to break into the operating system and get people's private information.

    Most smartphones and laptops, by themselves, search and connect to WiFi networks. They usually prefer a network with a connection that has been used before. Hackers' devices are able to record these searches and look like the trusted WiFi networks. When these smartphones and laptops log on to the networks which are not real, hackers can easily steal their private information.

    So next time, when we want to use our laptops or our smartphones in public places which offer free WiFi networks, please think it twice or take safe measures before using them.

    Do you often run outdoors to keep healthy? Have you ever thought about how running helps to clean up the earth? Sometimes a creative mind can bring us a win-win(双赢)situation.

    Plogging, a new way to exercise, began in Sweden(瑞典).The name "plogging" comes from two words the Swedish(瑞典的)word "plocka", which means" to pick up(捡起)", and the word" jogging", which means "to run slowly". A Swedish man called Erik started the movement. He saw rubbish here and there when riding to work each day. He became worried about the dirty environment and decided not to go to work by bike any more. Instead, he began to run to work and pick up the rubbish at the same time. To his joy, more and more people followed him and soon plogging became popular.

    Many people choose plogging instead of just jogging because they think plogging is a good way to help clean up the earth. Sometimes rubbish is difficult to collect because it may scatter all around. But if the runners pick up the rubbish on the way, it is quite different. After all, many hands make light work. Another reason is that plogging burns more calories(卡路里).According to a research, plogging for 10 minutes burns 48 calories, while usual jogging for 10 minutes burns about 39 calories.

    Everyone on the earth should play a part in cleaning it up! It's time for us to take action together. So ready? Let's plog tomorrow!

    Many objects in the universe are invisible, but they send radio waves. The radio telescope* thus appeared, and it is considered one of the greatest inventions in the twentieth century. Reber built the world's first radio telescope in 1937. Ryle and Hewish developed radio telescope systems for the location of weak radio sources, and they shared the Nobel Prize for Physics in 1974.

    A radio telescope is usually made up of:

    One or more antennas to collect the radio waves. Most antennas are made in the shape of a dish to collect and reflect, the radio waves to the sub—reflector, in the same way as a curved mirror focuses visible light to one point.

    A receiver and amplifier to receive the radio waves from the sub—reflector, and make these weak radio waves strong enough to be recorded and turned into electronic signals. To make an amplifier sensitive enough, it is usually cooled to, very low temperatures (e. g. as low as —270℃）.

    A recorder to keep a record of the electronic signals. Most radio telescopes today keep the signals to the computer's memory disk for astronomers to analyze later.

    Radio wavelengths are much longer than those of visible light, and the radio waves from deep space are always weak. To catch Radio wavelengths are much longer than those of visible light, and the radio waves from deep space are always weak. To catch these waves, radio telescopes usually have huge antennas. The sizes of most antennas in use today are around 50 to 300 metres in diameter. The antenna of FAST in Guizhou, China, the latest and largest radio telescope in the world, is 500 metres in diameter, as large as the size of 30 football fields.

    To avoid interferences, and keep the telescopes sensitive, radio telescopes are built in places where there are no human radio waves or electronic signals. For example, FAST is 5 kilometres away from the closest village and 25 kilometres away from the nearest town.

    Radio telescopes create pictures of the sky, not in visible light, but in radio waves. This is extremely useful, because there are objects that can't be seen, objects that we wouldn't even know without radio telescopes.

    Once people thought that dinosaurs were brown or gray in colour, but the answer is to be found out. After examining the remains of a dinosaur, scientists say the colour of the feathers is bright. American and Chinese scientists rebuilt the feathers of a flightless(不能飞的)dinosaur

that lived about 150 million years ago, and researchers studied melanosomes(黑素体)in the feathers. The researchers compared them to the melanosomes that control the colour of feathers on modern birds. They were then able to make out the colours of dinosaurs' feathers. Richard Prum, a biologist(生物学家)at Yale University, said the dinosaur would be a beautiful creature if it were still alive. The discovery is useful to scientists in another way. It helps them better understand not only how dinosaurs looked but also how they lived in their daily life. Some researchers plan to use this way to study the colours of other feathered dinosaurs.

    Now satellites(卫星)are helping to forecast(预报)the weather. They are in space and they can reach any part of the world.The satellites take pictures of the atmosphere(大气), because this is where the weather forms(形成). They send these pictures to the weather station. So meteorologists(气象专家)can see the weather of any part of the world. From the pictures, the scientists can often say how the weather will change.

    Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive new pictures, the meteor- ologists compare(比较)them with earlier ones. Perhaps they may find that the clouds have changed during the last few hours .This may mean the weather on the ground may soon change, too. In their next weather forecast, the meteorologists can say this.

    So the weather satellites are a great help to the meteorologists. Before satellites were invented, the scientists could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for 3 or 5 days. Soon, perhaps , they may be able to forecast the weather for a week or more ahead(提前)