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.

    Humans are much worse at estimating risk than we think we are. While we overestimate the risk of rare but disastrous occurrences, such as being attacked by a shark, many of us seriously underestimate the risk of behaviors that reduce our lifespan (寿命), such as smoking.

    In fact, there are two types of risks — acute and chronic. Acute risks are those that may kill you immediately, such as a car accident.

    Chronic risks don't kill you immediately but rob you of your life a little at a time. If you choose to eat an unhealthy diet, for instance, you may appear to be getting away with this, but you risk developing illnesses in future that may shorten your life.

    The problem is we value things much less when they occur in the future. Distant events are abstract — we don't know how and when they might affect us -~ so we care less about them.

    Take smoking for example. It is just about the worst choice you can make for your health. Every two cigarettes that you smoke takes 30 minutes off your lifespan.

    In contrast, eating vegetables is clearly very good for you, with each serve increasing your lifespan by two hours. This is a massive health gain and clearly should be a strong motivator for you to eat healthily.

    Drinking coffee is also good for you, though with limited health gains. Each cup of coffee (assuming you drink reasonably), is associated with approximately a ten-minute gain in your lifespan.

    Even drinking alcohol may add to your lifespan, with each serve adding 30 minutes to the length of your life. But this health gain is only true for the first drink; following drinks shorten lifespan. Alcohol also causes an acute risk when consumed in excess. Too much drinking gives you a 25 in one million chance of sudden death.

    We shouldn't be too nervous about exposure to risks. Life is all about making decisions about risks and rewards, and we all have a different starting point for what we consider acceptable risks to take. Even if we don't always make the healthiest decisions, at least we can make ones that are fully informed.

    An organization, Eye Care 4 Kids, is bringing much-needed eye care to poor kids. It provides free eye examinations for kids from poor families. Founded by Joseph Carbone in 2001, the organization has helped around 100,000 children in Utah and Nevada.

    Now, Cecil Swyers, a biomedical(生物医学的) engineer who was once a poor child himself, is bringing the charity's(慈善) services to poor students in Arizona, so that vision impairment(视力受损) doesn't stand in the way of their education.

    “Eye Care 4 Kids is bringing eye care and glasses to families that wouldn't have the means to pay for them,” said Mario Ventura from Isaac Elementary School District, the first school district in Arizona to receive its services.

    Good vision is important to a child's learning experience. According to a study, up to 80 percent of learning happens through sight for children between 6 and 18 years old. Without proper eye care, it's difficult for students to learn better and succeed.

    Swyers is hoping that by bringing the organization to Arizona he'll help a lot more students. He teamed up with two other organizations to get doctors to volunteer their time with the group. Using an Eye Care 4 Kids mobile clinic, Swyers visited Alta E. Butler Elementary School and has already helped 40 students.

    The school was grateful to receive the eye care, especially since the services came to them. “It's great for us,” said Assistant Principal Cindy Alonso.

    Swyers is hoping to bring Eye Care 4 Kids' services to other schools in the state. He said that hopefully his work will have a positive effect on students' futures. “If we can help students while they're young, we can make a difference in their futures,” he said.

    One of the questions surrounding climate change is how it might affect the food supply for a growing global population. A new study suggests that researchers have been overlooking how two key human responses to climate—how much land people choose to farm, and the number of crops they plant—will affect food production in the future. The new study focused on the Brazilian state of Mato Grosso, an emerging（新兴的）global breadbasket（产粮地区）that as of 2013 supplied 10 percent of the world's soybeans. The researchers used variations in temperature and precipitation（降水）across the state over an eight-year period to estimate the sensitivity of the region's agricultural production to climate change. Those historical comparisons can help in making predictions about the sensitivity of agriculture to future climate change.

    The study found that, if the patterns from 2002 to 2008 hold in the future, an increase in average temperature in Mato Grosso of just 1 degree will lead to a 9 to 13 percent reduction in overall production of soy and corn. “This is worrisome given that the temperature in the study region is predicted to rise by 2 degrees by 2050,” said Avery Cohn, who led the study.

    Most studies of this kind look only at the extent to which climate shocks affect crop output. But researchers can miss critical dynamics（动力）that can affect overall output, says Leah VanWey, one of the study's senior authors. “If you look at output alone, you're not looking at all of the information because there are economic and social changes going on as well,” said VanWey.

    If output decreases, farmers may put less land area into production because it's not profitable. Farmers may also vary the number of crops they plant in a growing season. Double cropping is common in Mato Grosso. But if the weather is bad, farmers may change their decision to plant a second crop.

    In the US, people prefer waiting for a table to sitting with people they don't know. This means a hostess may not seat a small group until a small table is available, even if a large one is. If you are sitting at a table with people you don't know, it is impolite to light up a cigarette first asking if it will disturb them.

    At American restaurants and coffee shops you are usually served tap water before you order. You may find the bread and butter is free, and if you order coffee, you may get a free refill.

    Most cities and towns have no rules about opening and closing time for stores or restaurants, though they usually do make rules for bars. Especially in large cities, stores may be open 24 hours a day.

    Serving in restaurants is often large, too large for many people. If you can't finish your meal but would like to enjoy the food later, ask your waitress or waiter for a "doggie bag". It may have a picture of a dog on it, but everybody knows you're taking the food for yourself.

    Supper and dinner are both words for the evening meal. Some people have "Sunday dinner". This is an especially big noon meal.

    Tips are not usually added to the check. They are not included in the price of the meal, either. A tip of about 15% is expected and you should leave it on the table when you leave. In some restaurants, a check is brought on a plate and you put your money there. Then the waiter or waitress brings you your change.

PhoneSoap: Charge and Clean Your Phone

    You may charge your phone every day, but do you clean your phone as much? Whatever your hands touch, your phones touch. It has been discovered that some phones have 18 times more bacteria and viruses than any surface in a public restroom. So it probably won't surprise you that a 2011 University of London study found that one in six of our phones have bacteria and viruses on them—specifically, the bacteria called E.coli.

    The research on bacteria and viruses led to the invention of PhoneSoap. It is not actually liquid like dishwasher soap. It is a phone charger that uses the electromagnetic radiation used in hospitals to kill 99.9 percent of bacteria and viruses, cleaning your phone while it charges.

    "There are really certain types of bacteria and viruses that we should not be in touch with, and they are really on our phones," says Wes Barnes, the PhoneSoap co-founder. It all started while his cousin and co-founder, Dan LaPorte, was in his cancer research lab at college. "He realized he got the idea of getting rid of bacteria and viruses on the phones," said Barnes. "In the lab they used UV-C light for destroying them. He realized this would be the fastest, most powerful way to kill any bacteria and viruses living on electronic machines."

    PhoneSoap looks like a little metal suitcase. Your phone rests in to charge and get cleaned at the same time. Instead of plugging your phone into the wall, you'd plug it into the PhoneSoap charger box. The process only takes a few minutes but, Barnes says, "The idea is that you can leave it in there overnight if you want to keep charging. Reflective paint keeps the light completely around the phone so it cleans the phone fully."

    The co-founders spent 2013 finding the right companies and they started shipping the product in late November. By last week's International Consumer Electronics Show in Las Vegas, PhoneSoap was all grown-up. Both co-founders have left their previous jobs and are selling PhoneSoap nonstop. "We're shipping almost more than we can handle each day," Barnes says. "It's been a great adventure."