Transparent animals let light pass through their bodies the same way light passes through a window. These animals typically live between 

the surface of the ocean and a depth of about 3,300 feet—as far as most light can reach. Most of them are extremely delicate and can be 

damaged by a simple touch. Sonke  Johnsen, a scientist in biology, says, “These animals live through their life alone. They never

touch anything unless they're eating it, or unless something is eating them.”

And they are as clear as glass. How does an animal become see-through? It's trickier than you might think.

      The objects around you are visible because they interact with light. Light typically travels in a straight line. But some materials slow and

 scatter(散射) light, bouncing it away from its original path. Others absorb light, stopping it dead in its tracks. Both scattering and absorption

 make an object look different from other objects around it, so you can see it easily.

But a transparent object doesn't absorb or scatter light, at least not very much, Light can pass through it without bending or stopping.

That means a transparent object doesn't look very different from the surrounding air or water. You don't see it —you see the things

behind it.

   To become transparent, an animal needs to keep its body from absorbing or scattering light. Living materials can stop light because they

contain pigments(色素) that absorb specific colors of light. But a transparent animal doesn't have pigments, so its tissues won't absorb

 light. According to  Johnsen, avoiding absorption is actually easy. The real challenge is preventing light from scattering.

Animals are built of many different materials—skin, fat, and more—and light moves through each at a different speed. Every time light

moves into a material with a new speed, it bends and scatters.Transparent animals use different tricks to fight scattering. Some animals are

simply very small or extremely flat. Without much tissue to scatter light, it is easier to be see--through. Others build a large, clear mass of

 non-living jelly-lie(果冻状的)material and spread themselves over it .

    Larger transparent animals have the biggest challenge, because they have to make all the different tissues in their bodies slow down light 

exactly as much as water does. They need to look uniform. But how they're doing it is still unknown. One thing is clear for these larger animals, staying transparent is an active process. When they die, they turn a non-transparent milky white.

    It was once common to regard Britain as a society with class distinction. Each class had unique characteristics.

    In recent years, many writers have begun to speak the “decline of class”and “classless society”in Britain. And in modern day consumer society everyone is considered to be middle class.

    But pronouncing the death of class is too early. A recent wide-ranging society of public opinion found 90 percent of people still placing themselves in particular class; 73 percent agreed that class was still a vital part of British society; and 52 percent thought there were still sharp class differences. Thus, class may not be culturally and politically obvious, yet it remains an important part of British society. Britain seems to have a love of stratification.

    One unchanging aspect of a British person's class position is accent. The words a person speaks tell her or his class. A study of British accents during 1970s found that a voice sounding like a BBC newsreader was viewed as the most attractive voice, Most people said this accent sounded “educated” and “soft”. The accents placed at the bottom in this study, on the other hand, were regional（地区的）city accents. These accents were seen as “common” and “ugly”. However, a similar study of British accents in the US turned these results upside down and placed some regional accents as the most attractive and BBC English as the least. This suggests that British attitudes towards accent have deep roots and are based on class prejudice.

    In recent years, however, young upper middle-class people in London, have begun to adopt some regional accents, in order to hide their class origins. This is an indication of class becoming unnoticed. However, the 1995 pop song “Common People” puts forward the view that though a middle-class person may “want to live like common people” they can never appreciate the reality of a working-class life.

    Sometimes the toughest thing about feelings is sharing them with others．Sharing your feelings helps you whether your feelings are wonderful or terrible．Sharing also helps you to get closer to people you care about and who care about you．But how?

    You can't tell your friends what's inside your backpack if you don't know what's in there yourself．Feelings are the same way．Before you can share them with anyone，you have to figure out what feelings you have．

    Making a list of your feelings can help．You can do this in your mind or by writing it out or even by drawing pictures．Is something bothering you? Does it make you frustrated or terrified? Do you feel this emotion only once in a while or much of the time?

    The way a person feels inside is important．If you keep feelings locked inside，it can even make you feel sick! But if you talk with someone who cares for you，you will almost always start to feel better．It doesn't mean your problems and worries magically disappear，but at least someone else knows what's bothering you and can help you find solutions．

    Your mom and dad want to know if you have problems and what's happening in your life．But what if a kid doesn't want to talk with parents? Then find another trusted adult，like a relative or a teacher at school．Maybe this person can help you talk with your parents about your problem or concern．

    Once you know who you can talk with，you'll want to pick a time and place to talk．You can talk publicly in your family．But some kids are more private than others and they will feel shy about sharing their feelings．Then find a quiet place or write it down on a piece of paper．A kid doesn't have to share every feeling he or she has．

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    In the summer of 1848, in Guatemala, a man called Ambrosio Tut went out into the jungle, as he did almost every day. Tut was a gum collector, looking for gum in the jungle. To do this, he had to climb the trees. One day, he got to the top of one tree and something caught his eye. He looked out across the trees and saw the tops of some old buildings.

    Tut didn't really know what he had seen but he knew it was something special. He ran to tell the local governor excitedly, and together they walked into the jungle. There they found Tikal, the city that the Mayans had built, many hundreds of years before. The two men saw pyramids, squares and houses.

    For a long time before that day, local people had known that somewhere in the jungle there was an old Mayan city. But no one had seen it for centuries. Between 200 and 900 AD, the city of Tikal had ben the centre of Mayan civilisation in the area, but then the Mayas let it—nobody knows why! After 1000 AD, the jungle began to cover it. And then people forgot that it was there.

    Seven years before Tut found Tikal, two British explorers had gone to Guatemala and had written a report about Mayan treasures in the jungle—but they hadn't mentioned Tikal. Even earlier than this, local Indians had told people about a great city hidden in the trees, but no one had listened to them. So they lost the chance to find the treasure. Now the lost city had been found again, and people went there immediately to see it.

    "Acting is the least mysterious of all crafts," Marion Brando once said. But for scientists, working out what is going on in an actor's head has always been something of a puzzle.

    Now, researchers have said actors show different patterns of brain activity depending on whether they are in character or not.

    Dr Steven Brown, from McMaster University in Canada, said, "It looks like when you are acting, you are suppressing (压制) yourself; almost like the character is possessing you."

    Brown and colleagues report how 15 actors, mainly theatre students, were trained to take on a Shakespeare role — either Romeo or Juliet — in a theatre workshop. They were then invited into the laboratory, where their brains were scanned in a series of experiments.

    Once inside the MRI scanner, the actors were asked to answer a number of questions, such as: would they go to the party? And would they tell their parents that they had fallen in love?

    Each actor was asked to respond to different questions, based on two different premises (前提). In one, they were asked for their own perspective, while in the other, they were asked to respond as though they were either Romeo or Juliet.

    The results revealed that the brain activity differed depending on the situation being tested. The team found that when the actors were in character, they use some third-person knowledge or inferences about their character.

    The team said they also found additional reduction in activity in two regions of the prefrontal cortex (前额皮质) linked to the sense of self, compared with when the actors were responding as themselves.

    However, Philip Davis, a professor at the University of Liverpool, was unimpressed by the research, saying acting is about far more than "pretending" to be someone — it involves embodying (体现) the text and language.

    THREE years ago Jenny Salgado, a Dominican shop assistant, moved to Highland town, a neighborhood of Baltimore. When she arrived the shop she works in, it was one of only a few Spanish businesses. Now there are many more. "It's good now if you speak Spanish," she smiles.

    Baltimore has been losing people for 60 years. To address this, its mayor, Stephanie Rawlings-Blake, wants to make it the most immigrant-friendly city in the world. Its libraries provide Spanish-language exercise classes. To help those with no papers, the city is introducing micro-loans (小额贷款) which require no credit checks; city police would no longer routinely check the immigration status of citizens or enforce any federal immigration law unless required to. The then governor, Martin O'Malley made it possible for illegal immigrants to get driving licenses.

    Such welcoming policies are spreading. Such cities as Cleveland, Dayton and Philadelphia all eagerly try to please immigrants. Rick Snyder, the governor of Michigan, has asked the federal government to offer 50,000 visas to people who agree to live in Detroit. His administration has made it easier for skilled migrants to get professional licenses.

    When a city's population falls, both tax receipts and services fall. Half-deserted neighborhoods breed (滋生) crime, driving yet more people to leave. No city has escaped this death circle without attracting new residents, says Steve Tobocman of Global Detroit.

    Several studies suggest that when immigrants arrive, crime goes down, schools improve and shops open up. In Detroit, immigrants living near the tiny separate city of Hamtramck have formed local watches to guard against thieves. Their neighborhoods are not just safer; they are also among the only places where it is as easy to buy fresh vegetables as drugs and alcohol.

    But attracting new immigrants to the cities which most need them is hard, argues Audrey Singer of the Brookings Institution. They care about the same things as everyone else: safe streets, good schools and jobs. Cities which have lost population for decades struggle with all of these.