From Asia to America and everywhere in between, Swing—an energetic form of dance that includes six-step and eight-step rhythms(节奏)—has taken the world by storm. Making a recent comeback, swing dance floors have popped up all over the world. Many clubs make fans of Swing happy by holding nights when swing music is played, and sometimes even offering classes to attract customers.

    Though Swing is now popular worldwide, it first appeared alongside the jazz movements of the 1920s and 1930s in New York City. While listening to jazz, the young black people of that time developed the movements of the Lindy Hop—a style of dance that is best known for a break away or "swing out" move and sudden improvisation(即兴表演).

    It was reportedly given this name when a reporter was interviewing a person at the dance hall who was watching other couples dance. When asked what that dance was called, the watcher looked at a newspaper next to him that had an article about Lindbergh—the first person to fly alone across the Atlantic(大西洋)—which was titled, "Lindy Hops the Atlantic". Then the watcher announced that the "Lindy Hop" was the name of the dance, and it has stuck since then.

    In 1926, the Savoy Ballroom was the first large business to offer a place for people to listen to swing music and dance. With its huge dance floor, the Savoy became a big success overnight, attracting some of the best dancers and musicians in the New York area.

    Within ten years, the Lindy Hops was sweeping through the United States and became a symbol of unity, as young people of all racial(种族的) backgrounds crowded into dance halls to swing the night away. Traditional dance teachers did not welcome it because they thought it was not even a real dance and were quite sure about its demise but Swing has proved them wrong; it continues to be one of the world's most fun dances.

Here is some cool information about the world's population. 

The late president of South Africa, Nelson Mandela, once said: "If you talk to a man in a language he understands, that goes to his head. If you talk to a man in his own language, that goes to his heart. "

Mandela understood that our mother language is a very close thing to us. For people who speak an ancient tongue as their mother language, it helps them keep their traditions. Their language is their main connection with their ancestors(祖先). 

So it's a serious thing when a language disappears. Over the last century, more than 400 languages have died out. Some languages are now spoken only by a few dozen people, like Yagan in Chile. Africa and South America are also places where many languages are dying. 

Why are humans speaking fewer languages than we once did? The answer has to do with globalization (全球化). Nowadays, it's more useful to speak certain languages - English is one example - rather than others. This has killed some languages, usually ones spoken by fewer or less influential people. 

But some people aren't prepared to accept a planet with fewer and fewer languages. The United Nations has set Feb 21 as International Mother Language Day. The organization wants people to pay more attention to dying languages. 

This work is very important. As US writer Rita Mae Brown wrote, "Language is the roadmap of a culture. It tells where its people come from and where they are going. "

If you've ever seen elephant seals(象海豹) lying on a beach, you might think all they do is sleep. But now scientists have discovered that when elephant seals are in the ocean, they hardly sleep at all. They just sleep for about two hours a day.

Even though elephant seals are large animals, they have to be careful in the ocean. Near the surface(水面), predators like sharks and orca s are a danger. So elephant seals spend most of their time diving(潜水) deep underwater, looking for food. Usually, they will dive for about 30 minutes, then come up for air for just a couple of minutes before diving again.

Scientists have wondered how elephant seals can sleep while they're at sea, since they are almost diving all the time. Animals like dolphins and sea lions have a special way. One half of their brain can sleep, while the other stays awake. But elephant seals are like humans- both halves of the brain need to go to sleep at the same time. So how do they sleep?

To find out, a scientist named Jessica Kendall- Bar did a research. She created a special cap that could record the elephant seals' brain activity. The cap also collected information on the elephant seals' heart rates, how their bodies were moving, and how deep they were. Dr. Kendall- Bar and her team put the caps on thirteen young female elephant seals.

The scientists learned that elephant seals steep in short times while they are diving. They only sleep for about 10 minutes at a time. They wake up in time to go up for more air. The scientists found that elephant seals only sleep for about two hours a day when they're in the ocean. That means that the rest they get once they return to land is very important, which helps them have energy again. Back on land they sleep for about 10.8 hours a day

The researchers hope that their work will help to protect the places where elephant seals sleep when they're on land.

We see many things like colors, lights, buildings with our eyes. But can you protect (保护) your eyes well? {#blank#}1{#/blank#}

Let eyes have a good rest.

Many people need to look at a computer when they work or study. That puts a lot of pressure (压力) on their eyes. So every 20 minutes, you should let your eyes have a good rest for around 20 seconds. {#blank#}2{#/blank#}

Wear a sun hat or sunglasses.

{#blank#}3{#/blank#} They can be bad for eyes, so it's best to get in the habit of protecting them from an early age. Wearing a sun hat or sunglasses is the best way to protect your eyes.

Have eye-friendly food.

You can also protect your eyes by eating some eye-friendly food.{#blank#}4{#/blank#}

Have a good sleep.

{#blank#}5{#/blank#} You may think you are doing nothing when you're sleeping. But it's the time for your body to rebuild and repair (重建和修复). At night, your eyes keep cleaning out the bad things that come in during the day.

根据材料内容，从下面五个选项中选出能填入文中空缺处的最佳选项，使文章意思通顺、内容完整。