Have you ever experienced the feeling of falling as you start to fall asleep? Sometimes you may come to realize this feeling. If so, don't worry. Many people have felt the same thing.

In fact, these muscle twitches (肌肉抽搐) in the arms, legs or other parts of the body are called hypnic jerks (入睡抽动) or sleep starts. And they are very common. Up to 70 percent of people experience them sometimes, Huffington Post reported. But what causes it?

There are some theories(理论). Some scientists believe that the feeling of falling comes from the body relaxing itself, especially if the person is anxious or unable to get comfortable. As you're about to sleep, your muscles become relaxed. But your brain stays awake. It misunderstands the relaxing of your muscles as a sign that you're falling. Then the brain jerks the body awake as if it's trying to protect you.

    Other scientists believe that different phases of sleep might cause the hypnic jerks. When we sleep, we experience two phases: non-rapid eye movement (NREM) and rapid eye movement (REM). During REM, our heart rate (心率), breathing and nervous system can act irregularly (不规律地). If the body experiences flashes (一瞬间) of REM while entering sleep, these irregularities could cause twitches.

If you don't want to experience hypnic jerks, scientists have some suggestions. When you become deeply relaxed, you can learn how to reconnect slowly by moving your fingers and toes a little bit. Then start to move your head and open your eyes, while being aware of yourself as you get out of the relaxed state.

    But experts agree that hypnic jerks, though sometimes scary, are harmless. If it wakes you up, simply roll over and go back to sleep. But keep in mind: a caffeinated (含咖啡因的) drink, exciting evening activities or stress may make hypnic jerks happen more often.

    There are many wetlands in China and some of them have become the world's important wetlands. The Chinese Yellow Sea Wetlands are among them. They are in Yancheng, Jiangsu Province. They are home for many different kinds of birds and animals. The world's largest Milu Deer Nature Reserve(自然保护区) is in them. More than700 milu deer live freely there. There are not many red—crowned cranes in the world, but every winter you can see some in the Red—crowned Cranes Nature Reserve in the Yellow Sea Wetlands.

    The temperature in the wetlands is usually neither too high nor too low. There is a lot of rain and sunshine, too. They are usually good places for wildlife. Offering food and home for some special kinds of animals and birds is not the only reason why we need to protect wetlands. Wetlands are important because they also prevent(阻止) flood(洪水). But some people want to change the wetlands to make more space for farms and buildings. This means there will be less and less space for wildlife.

    Luckily, more and more people are beginning to realize(意识到) the importance of wetlands and wildlife. Every year, on February 2^nd, many activities are held to tell people more about wetlands.

    Read the questions and answer YES or NO, then you will find out how good you are.

⒈When you don't understand something, you ask questions.

⒉You like listening to older people talk about the past.

⒊You think that you can learn something interesting from everyone around you.

⒋You are brave enough when you have to talk to people you don't know.

⒌You enjoy reading books about famous people.

⒍You always see and talk to different people.

⒎You are interested in learning new ways of doing things.

⒏You enjoy sharing experiences with friends and learning from people of all ages.

⒐You talk a lot about yourself.

⒑Even if you are often wrong, you make your own decisions.

⒒You hate teaching what you are good at: sports, technology and so on.

⒓Your parents don't understand you, so you don't talk to them much.

Score Now! (开始计分 )

    Score2 points if you answer YES to each of the first 8 questions, and 0 if you choose NO.

    Score 2 points if you answer NO to each of the last 4 question, and 0 if you choose YES.

    18-24. You are friendly and open-mind. You make people feel important by listening to what they have to say. You'll probably succeed in learning all kinds of interesting things.

    10-16. Remember that every single person you know can teach you something. You will great make your life rich and colorful.

    0-8 About 400 years ago, a famous writer wrote, “No man is an island.” This is still true today. Try to be more open and interested in people around you.

    When he was nine years old, an American boy called Milo Cress had a question: How many plastic straws (吸管)do Americans use every day?

    He quickly learned there wasn't a simple answer. The boy tried to find it out himself. Through lots of research, Cress found out that Americans use about 500 million straws every day. In hopes of cutting down plastic waste, he founded the Be Straw Free project in 2011.

    Cress started the project in his hometown Burlington. Vermont. He asked a local restaurant to stop offering straws with every drink order. It was a simple change. However, it would save money. And by doing that, the restaurant would cut down on its straw use by 50 percent.

    For the year that followed, Cress tried to spread his project across the United States. More and more restaurants agreed to join. They stop providing the customer with a straw unless he or she asks for one. Last April, Seattle became the first American city to completely ban plastic straws.

    After his project became popular, Cress took his findings on the road. He has spoken to tens of thousands of students around the world. He wants to encourage more people to say no to plastic straws.

    "Focusing on straws is one simple step we all could take," Cress says. "And it makes me feel that I, as a kid, could make a difference, too."

    Everyone knows the strange feeling of your fingers wrinkling up (起皱) when they're wet. Sometimes when in water, it seems as if your hands have aged 30 years in a second. But is this an accident? Or is it something that nature has built into our bodies?

    Scientists at the University of Newcastle in the UK recently did a test. They asked people to pick up things (some wet and some dry). And take them from one place to another. Some people did this with dry hands, while others had to leave their hands in water for 30 minutes first so that their skin was wrinkled. The study found the second group with wet hands had an advantage when carrying things that were also wet.

    The scientist Tom Smulders said that "this wrinkling of our fingers in wet conditions could have helped with gathering food from wet vegetation or streams". Wrinkling happens when blood vessels contract (血管收缩) and pull the skin back.

    A long time ago, humans lived a very difficult life in a brutal world, where the smallest advantage could make a huge difference. Having wrinkled skin might have helped people catch fish. This would help them get through the winter. These humans would then have had an advantage. Their genes would be accepted by natural selection.