How do you study each day? You may answer it in one second: have classes at school, take notes and do homework. Feeling a little bored? There are other ways that can make learning interesting and varied. It's called digital learning.

    Digital learning is a way to help students learn by using the Internet. There are three important kinds of digital learning. Apps are computer software applications (应用). People can download them on their mobiles. The other two kinds are social networking services, including weibo and WeChat and websites. Every one of them is like your teacher. They help you master what you learn at school.

    Compared with traditional learning ways, digital learning has its advantages. Digital learning is also varied. It covers almost every school subject. More importantly, it always offers students the newest resources (资源) to learn from.

    Digital learning is also personalized. You can choose what you like to learn. If you don't master what you have learned at school, you can learn again through digital ways.

    However, digital learning also has disadvantages. When you use digital ways to learn, you've got little chance of talking with teachers and classmates. As digital learning uses computers or smartphones, watching the screen too long may be bad for your eyes. It is better to take a rest every 20 minutes.

    Many animals do strange things before an earthquake. This news may be important. Earthquakes can kill people and knock down homes. The animals may help to save lives.

Some animals make a lot of noise before an earthquake. Farmers have told about this. Dogs that are usually quiet have started to bark(吠). Horses on farms have run around in circles. Mice have left their holes and run away. Cows have given less milk.

In a town in Italy, cats raced down the street in a group. That happened only a few hours before an earthquake. In San Francisco, a man kept tiny pet frogs. One Sunday, the frogs jumped around more than ever. They made loud noises, like bigger frogs. That night, an earthquake struck the city.

    People want to know when an earthquake is coming. Then they could get away safely. Right now, there is no sure way to know ahead of time. Maybe the best idea is watching the animals.

    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.