A Samoan airline says that it is the world's first carrier to charge passengers by their weight. Samoa Air, which opened in 2012, asks passengers to give their personal weight during booking, which is then charged according to the length of a flight. The customers will also be weighed just before they board the plane.

    "It is believed that all people throughout the world are the same size," Samoa Air CEO Chris Langton said. "Airplanes always run on weight, not seats."

    "There is no doubt in my mind that this is the concept of the future. This is the fairest way of your travelling with your family or yourself."

    Though the airline introduced the plan last November, it caught people's attention last week when the carrier began international flights to neighboring American Samoa.

    Almost at the same time, a Norwegian economist, Bharat Bhatta, published a report suggesting that airlines should charge obese passengers more.

    The Pacific Islands contain some of the world's most common countries for obesity, many ranking in the top 10, according to the World Health Organization (WHO). Samoa is ranked number four, with 59.6 percent of the population considered obese, said the most recent WHO report.

    According to Samoa Air's latest schedule, the airline charges up to $0.57 per kg for flights in Samoa and $1.03 per kg for its only international flight to American Samoa, around 250 miles.

    Children under 12 are charged 75 percent of the adult rate, with fares also based on weight. Any overweight baggage is calculated at the same rate as the passenger's personal weight.

    The plan could actually prove cheaper in some cases, such as for families travelling with small children, and Langton said customer reaction has mainly been "amazingly positive".

    The idea of charging passengers by weight has been hotly discussed before, and in the US some airlines require those who do not fit into a seat comfortably to buy a second seat.

                                                      Four Wild Animal Species Were Endangered

    Maybe you can still see them at the zoo. But that doesn't mean they're doing alright in the wild.

    Tigers

    All six tiger species are endangered, with Suatran tigers and South China tigers at a seriously endangered status. The main reasons for their population decline are illegal hunting and destroyed habitats, as humans clear forests to gather timber and build roadways. Only about 3890 tigers presently live in the wild.

    Ground squirrels

    That's right, even squirrels are endangered, specifically the San Joaquin ground squirrel. Native to California, USA, these guys have been disappearing since 1979 on account of the construction and human developments going through their habitat. Their total population is unknown, but it could be anywhere between 124000 and 4130000.

    Giraffes

    The International Union for the Conservation of Nature recently put giraffes at a vulnerable status, the level just before endangered. The giraffe population has declined 40 percent in the last 30 years, primarily due to loss of habitat and illegal hunting. Some giraffes are killed just for their tails, which are considered status symbols in Africa.

    Asian elephants

    The main threat to Asian elephants, one of the most intelligent animals, is their shrinking habitat. As the human population grows, people invade their land to build roads and railway tracks. Elephants in Myanmar are at an especially high risk for being captured and traded or used illegally in the tourist industry. Fewer than 50000 are left on the entire continent.

    Everglades National Park (大沼泽地国家公园) is located in the state of Florida. It is the largest wilderness in the entire country and makes up 25% of the wetlands in the state. The park is home to several rare and endangered species. It is also the third largest national park in the US, after Death Valley and Yellowstone. Each year, about 1 million tourists visit the park. On a global level, it has been announced as a World Heritage Site.

    Unlike most other national parks, Everglades National Park was created to protect an ecosystem (生态系统) from damage. In 1947, President Harry Truman spoke at the official opening of Everglades National Park, saying the goal of creating the park was to protect forever a wild area that could never be replaced.

    10,000 different islands make up Everglades National Park. Each of these islands is lived by natural wildlife. The Everglades is home to about 15 species that are endangered. In addition, more than 350 bird species and 300 species of fresh and saltwater fish live within the park. The Everglades is also home to 40 species of mammals and 50 reptile species.

    There are many ways to explore the Everglades. Visitors can see alligators (短吻鳄) while hiking the Anhinga Trail. The Everglades is one of the only places on Earth where freshwater alligators and saltwater crocodiles live in the same area. Visitors using airboats are likely to see large groups of birds. Some visitors might enjoy riding bicycles through Shark Valley. Others may want to move slowly through waters where they can see insects and wildlife closely.

    According to experts, changes to the Everglades are becoming a danger to several different kinds of wildlife. They say it is a result of actions the US government began more than 50 years ago, and settlers began even earlier.

    Whenever we see a button, we are eager to press it because we know something will happen. This is true in most cases, for example on a doorbell and on the "on/off" button on the TV. But some buttons are actually fake, like the "close" button on a lift.

    Many people are in the habit of pressing the "close" button because they don't have the patience to wait for the lift doors to shut. But lifts "close" buttons are a complete scam, at least in the US-the doors will not close any faster no matter how hard you press.

    It started in the 199os when the Americans with Disabilities Act was passed in the US, making sure that all lifts stayed open long enough so that people with disabilities could enter. Only US firefighters and repairmen can use the buttons to speed up the door-closing process if they have a code or special keys.

    But to normal lift riders, the buttons aren't completely useless. According to psychologists, fake buttons can actually make you feel better by offering you a sense of control." Perceived（能够感知的）control is very important. It reduces stress and increases well-being," Ellen J. Langer, a psychology professor, said," Having a lack of control is associated with depression."

    Experts have revealed that a lot of buttons that don't do anything exist in our lives for this same purpose. For example, many offices in the US have fake thermostats（温度调节器）because people tend to feel better when they think they can control the temperature in their workspace.

    But psychologists found it interesting that even when people are aware of these little" white lies", they still continue to push fake buttons because as long as the doors eventually close, it is considered to be worth the effort.

   "That habit is here to stay," John Kounios, a psychology professor, said," Even though I have real doubts about the traffic light buttons, I always press them. After all, I've got nothing else to do while waiting.  So why not press the button in the hope that this one will work?"

    Donald was not very good at math. He could not understand the teacher's explanations. Even when the teacher explained something a second time, Donald still could not understand it. "Never mind," Donald told himself, "I'm quite good at other subjects. I'll cheat in the math exam, and then I won't be in trouble."

    "I will sit next to the boy who's good at math,'' he thought, "and copy down his answers." The day of the exam came, and Donald sat next to Brian Smith, who was always at the top of the class in math. Donald carefully copied Brian's answers onto his own exam paper. At the end of the exam, the teacher collected the papers and graded them. Then she said, "Well, boys and girls. I've decided to give a prize to the student who got the highest grade. However, it's difficult for me to decide who to give the prize to, because two students, Donald and Brian, got the same grade."

    "Let them share it,'' one of the other students said.

    "I have thought about that,'' the teacher said, "but I have decided to give the prize to Brian." Donald was angry when he heard this. He stood up and said, "That is not fair. I got the same grade as Brian." "That is true," the teacher said. "However, Brian's answer to Question 18 was 'I don't know', while yours was 'Neither do I'."

    Rivers are earthly arteries(要道) for the nutrients, deposits and freshwater that sustain healthy, diverse ecosystems. Their influence extends in multiple dimensions—not only along their length but below­ground to aquifers(蓄水层) and periodically into nearby floodplains.

    They also provide vital services for people by fertilizing agricultural land and feeding key fisheries and by acting as transportation corridors. But in efforts to ease ship passage, protect communities from flooding, and draw off water for drinking and irrigation, humans have increasingly constrained and broken these crucial water ways. “We try to control rivers as much as possible,” says Gunther Grill, a hydrologist at McGill University.

    In new research published in May in Nature, Grill and his colleagues analyzed the barriers to 12 million total kilometers of rivers around the world. The team developed an index(指数) that evaluates six aspects of connectivity—from physical fragmentation (by dams, for example) to flow regulation (by dams or levees) to water consumption—along a river's various dimension. Rivers whose indexes meet a certain threshold(临界值) for being largely able to follow their natural patterns were considered free­flowing.

    The researchers found that among rivers longer than 1,000 kilometers (which tend to be some of those most important to human activities), only 37 percent are not blocked along their entire lengths. Most of them are in areas with a minimal human presence, including the Amazon and Congo basins and the Arctic. On the contrary, most rivers shorter than 100 kilometers appeared to flow freely—but the data on them are less comprehensive, and some barriers might have been missed. Only 23 percent of the subset of the longest rivers that connect to the ocean are uninterrupted. For the rest, human infrastructure is starving estuaries(河口) and deltas (such as the Mississippi Delta) of key nutrients. The world's estimated 2.8 million dams are the main cause, controlling water flow and trapping deposits.

    The new research could be used to better understand how proposed dams, levees and other such projects might impact river connectivity, as well as where to remove these fixtures to best restore natural flow. It could also help inform our approach to rivers as the climate changes, says Anne Jefferson, a hydrologist at Kent State University, who was not involved in the work. Existing infrastructure, she says, “has essentially been built to a past climate that we are not in anymore and are increasingly moving away from.”