Winter is very cold in many countries. It's easy for you and me to keep warm. If we are cold, we can just buy a warm coat or use a heater and we will feel better. But what about animals? How do they keep warm in winter?

    Some animals migrate(迁移). This means they travel to places where the weather is warmer. Many birds leave before the winter starts. They fly in groups. If they fly together, the trip will be safer. They like to migrate to the same places every year. Do you know how they can find the same places? Scientists say that birds use the sun, moon and stars to help them. Other animals like moose (麋鹿) also migrate. Fish and whales swim to warmer water.

    Some animals don't have leave their homes. They hibernate in winter. They fall into a very deep sleep. The animals' temperature drops and their breathing slows down. Before the winter, these animals must eat too much food that they get very fat. If they don't eat enough, they may die when they are hibernating.

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    Most people hope to have a memory which helps them succeed in study, work and life. Can memory be improved? Luckily, hundreds of studies in the past 50 years have already given us a definite answer.

    A healthy lifestyle keeps our brain young and memory sharp. First of all, it is necessary to have a healthy diet. Eating more food rich in B vitamins and vitamin E, such as vegetables and lean meat, helps you have a better memory. Doing exercise can keep your brain alive, too. Proper exercise provides much oxygen for the brain. Running, riding a bike, swimming and even walking two or three times a week are helpful. Moreover, getting enough sleep is important. Only when your brain gets a good rest, can it work well. The healthier your lifestyle is, the better your memory will become. But do not expect a sudden change－it takes a long time to make a difference.

    Memory stills help you remember things better. The following three are the most widely used. Chunking is a way of remembering a piece of information by cutting it into small ones. For example, to memorize a ten-digit telephone number 2127983630, you can divide the digits into three groups: first 212, then 798, and lastly 3630. This method is far more effective than remembering a string of 10 digits. Organization means organizing information into groups of the same kind. For example, trees, grass and flowers are plants; tigers, pandas, horses and cows are animals. Imagery is remembering newly learnt information by using your imagination and connecting it with something that you are familiar with.

    However, memory skills will hardly work if you don't understand the information. What's more, only a regular review can make the memory last long. That is why students are always advised to go over what they have learnt and then use it as regularly as possible.

    Human brains are like muscles that needs nutrients and exercise to become stronger. If you make a few lifestyle changes and try some memory skills, you can certainly improve your memory.

    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.

    There is a lot of salt on the Earth, and it mixes very well with water.

There is some salt in all water. Water on the land runs into lakes and rivers. These rivers run into the seas and oceans. They carry a little salt with them. Some of the ocean water moves into the air and clouds. It evaporates. Salt cannot evaporate. It stays in the oceans.

    The water in the oceans has more salt than river water. There is about 3. 5% salt in the ocean water. Some seas have more salt than others.

    Some of the water leaves the lakes. It evaporates, but the salt cannot. These lakes are very salty. There are two famous lakes like this. They are the Dead Sea in the Middle East and the Great Salt Lake in Utah(犹他州）in the United States. They are much saltier than the Atlantic Ocean（大西洋）and the Pacific Ocean(太平洋）.

    Smartphone apps certainly make our lives easily. However, sometimes they can also cause problems.

    Recently, the Ministry of Education(教育部) announced that teacher should not use Wechat or QQ to give homework or ask parents to grade kids's homework.

    Many teachers in China depend heavily on apps to give homework. The kids have to do their homework, stare at a phone screen. For example, Liu Yanming, a sixth-grade student in Shanghai, usually has to use his mother mobile phone to do his homework. Liu Yong, his father is afraid that apps could distract kids by encourage them to watch something unrelated(无关) to homework. "He is just 12 years old, and I do not want to buy him a cellphone," Liu told China Daily. "I also worry that my son's eyesight will be hurt because of staring at the phone for too long."

    However, Bai Yueping, president of Shanghai Tangzhen Middle School, defended (辩护) using apps for homework. Parents can understand their kids' learning situation and supervise (监督) them to finish the homework, Bai told China Daily.

    Zhang Siqi is a student from Renmin University of China.       "The use of WeChat or QQ to give homework is convenient," Zhang told China Daily. "We're living in an Internet era （时代）. It's unwise to refuse to take advantage of technology."

    Chu Zhaohui, a researcher at the National Institute of Education Sciences, believed that it is impossible to stop the use of electronic devices(设备) in the Internet era. However, students should use them when it's necessary, such as when they do listening exercises. "We don't want to stop outline education models, but they must be used carefully. Modern technologies are good... but they should not steal the show(喧宾夺主) ," he told China Daily.