From the modern London Eye to the historic Tower of London, below are London's most visited tourist attractions. Many of London's top attractions are free, making them affordable places to learn about some culture. Whether you prefer history or modern art, you'll find it at one of these must-visit spots.

British Museum

    The world-famous British Museum exhibits the works of man from prehistoric to modern times, from around the world. The most interesting and exciting parts include the Rosetta stone, the Parthenon sculptures and the mummies in the Ancient Egypt collection. Some exhibitions require tickets.

National Gallery

    The greatest and most beautiful building of Trafalgar Square, London's National Gallery is a vast space filled with Western European paintings from the 13th to the 19th centuries. In this impressive art gallery you can find works by masters such as Van Gogh, da Vinci, Botticelli, Constable, Renoir, Titian and Stubbs. Some exhibitions require tickets.

Tate Modern

    Sitting on the banks of the Thames is the Tate Modern, Britain's national museum of modern and contemporary art. Its unique shape is due to it being a power station before. The gallery's restaurants offer wonderful views across the city. Some exhibitions require tickets.

Coca-Cola London Eye

    The Coca-Cola London Eye is a major feature of London's skyline. It has some of London's best views from its 32 capsules, each weighing 10 tonnes and holding up to 25 people. Climb aboard for a breathtaking experience, with an unforgettable view of more than 55 of London's most famous landmarks -- all in just 30 minutes!

Madame Tussauds

    At Madame Tussauds, you'll come face-to-face with some of the world's most famous faces. From Shakespeare to Lady Gaga you'll meet influential figures from show business, sport, politics and even royalty. Strike a pose with Usain Bolt, get close to One Direction or receive a once-in-a-lifetime audience with Her Majesty the Queen.

    In colleges around the country, most students are also workers. The reality of college can be pretty different from the images presented in movies and television. Instead of the students who wake up late, party all the time, and study only before exams, many colleges are full of students with pressing schedules of not just classes and activities, but real jobs, too.

    This isn't a temporary phenomenon. The share of working students has been on the rise since the 1970s, and one-fifth of students work year round. About one-quarter of those who work while attending school have both a full-course load and a full-time job. The arrangement can help pay for tuition (学费) and living costs, obviously. And there's value in it beyond the direct cause: such jobs can also be critical for developing important professional and social skills that make it easier to land a job after graduation. With many employers looking for students with already-developed skill sets, on-the-job training while in college can be the best way to ensure a job later on.

    But it's not all upside. Even full-time work may not completely cover the cost of tuition and living expenses. The study notes that if a student worked a full-time job at the federal minimum wage, they would earn just over $15,000 each year, certainly not enough to pay for tuition, room, and board at many colleges without some serious financial aid. That means that though they're sacrificing time away from the classroom, many working students will still graduate with at least some debt. And working full time can reduce the chance that students will graduate at all, by cutting into the time available for studying and attending classes.

    There is little reward for attending but not finishing college. Students who end up leaving school because of difficulty in managing work and class are likely to find themselves stuck in some of the same jobs they might have gotten if they hadn't gone at all. The difficulty of working too much while in school can create a cycle that pushes students further into debt without receiving any of the financial or career benefits.

    An Israeli law banning too skinny models went into effect with the start of 2013. The law, approved last March in Israel, requires models to prove they have maintained a Body Mass Index (BMI) of at least 18.5 for three months before a fashion show. That means a woman who is 68 inches tall can weigh no less than 119 pounds.

    "This law is another step in the war against eating disorders," said physician Adatto. "Underweight models," he explained, "can no longer serve as role models for innocent young people who copy their false image of being skinny."

    But some critics in this country say it is misguided, focusing on weight instead of health. They also say the Israeli ban is bound to fail because of the strong power of the fashion industry. "I think it's an approach that isn't going to work." said eating disorder expert Susan Ice, who worked with an organization which creates a healthy working environment for models.

    But Adatto told the reporter that he began to concern the issue after meeting an ambitious model who looked like she needed to be hospitalized. He said. "I realized that only legislation(立法) can change the situation. There was no time to waste; so many girls were dieting to death."

    However, the efforts to regulate models' weight in Spain and Italy have not resulted in significant changes in part because of difficulties in determining reliable methods of measuring weight and health.

    Still, folks including Ice say there's no denying that images from Hollywood and the fashion industry can be difficult for young women to deal with. "Certainly I don't believe the modeling industry has caused the rise in eating disorders, but it makes it harder," she says. "It's a difficult recovery environment, worshiping thinness as the beauty ideal."

    The skin under the eyes is delicate, which is why it sometimes appears sunken and has darker coloring than elsewhere on the face. Aging and health problems play a role in sunken eyes but other factors can contribute, so it may affect younger people as well.

Dehydration

    The most common cause of sunken eyes is dehydration, or not having enough water in the body. Consuming too much coffee, soda, and prepackaged drinks may increase production of urine(尿液), which may lead to dehydration.

    Vitamin shortages

    Shortages of vitamin C, vitamin K, and iron can cause eyes to become sunken. Vitamin C helps with absorbing iron and decreasing bruising(瘀斑), while vitamin K is responsible for blood thickening, causing unhealthy skin. Easy bruising and unhealthy skin will result in sunken eyes.

    Weight loss

    Most people tend to lose weight in their face first. Sometimes, the weight loss is sudden enough to make blood vessels(血管)below the eyes easy to see, and the skin clear, producing the appearance of sunken eyes. Sudden weight loss may also cause nutritional shortages, which can lead to sunken eyes.

    Not enough sleep or poor quality sleep can cause sunken eyes and a person's DNA or the habit of smoking can also contribute to sunken eyes. Most cases of sunken eyes relate to the quality of an individual's nutrition and healthy living. When these causes are corrected, sunken eyes can be resolved without further treatment. This means that causes can be avoided or treated in good time to prevent the recurrence of sunken eyes.

    A shark moving around the coastline is normally a worrying sight，but this waterborne drone (无人机) threatens floating rubbish instead of people.

    Developed by Dutch company RanMarine, the WasteShark takes nature as its inspiration with its whale shark-like mouth. Responsible for collecting waste, the drone will begin operations in Dubai Marina in November after a year of trials with local partner Ecocoast.

    According to RanMarine, the WasteShark is available in both autonomous and remote-controlled models. Measuring just over five feet by three-and-a-half feet (1.5 meters by 1.1 meter), it can carry up to 352 pounds of rubbish (159.6 kg) and has an operational battery life of 16 hours.

    By 2016 there were approximately 150 million tons of plastic in the world's oceans. One paper from December 2014 estimated that over a quarter of a million tons of ocean plastic pollution was afloat.

    "WasteShark also has the abilities to gather air and water quality data, remove chemicals out of the water such as oil, and heavy metals, and scan the seabed to read its depth and outlines," said Oliver Cunningham, one of the co-founders of RanMarine. "Fitted with a collision-avoidance system, the drone uses laser imaging detection and ranging technology to detect an object in its path and stop or back up if the object approaches."

    "Our drones are designed to move through a water system, whether it's around the perimeter (周边) or through the city itself. The drones are that last line of defense between the city and the open ocean," added Cunningham. "WasteSharks are operating in Dubai, South Africa and the Netherlands and cost $ 17, 000 for the remote-controlled model and just under $ 23, 000 for the autonomous model."

    Dubai-based operator Ecocoast has two WasteShark drones. Co-founder Dana Liparts says they will clean waterfronts for clients including hotels and environmental authorities and that Ecocoast' intention is to have the collected rubbish recycled or upcycled. However, Liparts argues that cleaning waterways doesn't have a one-size-fits-all solution and requires a combination of new technology, preventative measures and changing people's attitudes towards littering.

    Plants are boring. They just sit there photosynthesizing (光合作用) while animals have all the fun. Right? Not so much. A new study has found that there is a long history of interactions between ants and plants. The ant and plant co-evolution (协同进化) started with ants feeding on plants and plants evolving ant-friendly features.

    Plants make a number of different structures that are specific for ant use. Some plants have evolved features that persuade ants into defending them from attack from other insects and even mаmmаlѕ. Тhеѕе іnсludе hollow thorns that аntѕ will live іnѕіdе, or ехtra nесtаr (琼浆) оn lеаvеѕ or stems for the ants to eat. Some ants will just cheat and take the nectar and run, but some will stick around and attack anything that tries to hurt the plant. Other plants get ants to help them move their seeds around, by providing them with rich food packets attached to the seeds. The ant will pick up the seed and carry it away, eat the food packet, and leave the seed—often in a nutrient-rich area where it'll grow better, and since it's farther away from its parent, they won't have to compete for resources.

    But scientists weren't sure how the evolutionary relationship between ants and plants got started. If evolution is an arms race between species developing ways to make use of their neighbors, then scientists wanted to know whether plants or ants fired the first shot. It was a chicken-and-egg question, whether things started with ants developing behaviors to take advantage of plants, or plants evolving structures to take advantage of ants.

    The history of ants and plants evolving together goes back to the time of the dinosaurs, and it's not easy to tell from fossils who fired the first shot. However, it is a question of little significance. Scientists say their study maters because it provides a look at how these widespread and complex interactions evolved.