Almost every machine with moving parts has wheels, yet no one knows exactly when the first wheel was invented or what it was used for. We do know, however, that they existed over 5,500 years ago in ancient Asia.

    The oldest known transport wheel was discovered in 2002 in Slovenia. It is over 5,100 years old. Evidence suggests that wheels for transport didn't become popular for a while, though. This could be because animals did a perfectly good job of carrying farming tools and humans around.

    But it could also be because of a difficult situation. While wheels need to roll on smooth surfaces, roads with smooth surfaces weren't going to be constructed until there was plenty of demand for them. Eventually, road surfaces did become smoother, but this difficult situation appeared again a few centuries later. There had been no important changes in wheel and vehicle design before the arrival of modem road design.

    In the mid-1700s, a Frenchman came up with a new design of road—a base layer (层) of large stones covered with a thin layer of smaller stones. A Scotsman improved on this design in the 1820s and a strong, lasting road surface became a reality. At around the same lime, metal hubs (the central part of a wheel) came into being, followed by the pneumatic tyre(充气轮胎) in 1846. Alloy wheels were invented in 1967, sixty years after the appearance of tarmacked roads (柏油路). As wheel design took off, vehicles got faster and faster.

    Recently I had a conversation in Beijing with an adult Chinese friend who was complaining how difficult it was to study English. No surprises there. It is a difficult language to master, just like Chinese. I made a few suggestions based on my experience. One involved a very valuable fact which I learned from my high school Latin and Greek teacher, Dr. Smith．He is a gifted linguist （语言学家），and has an amazing ability to remember things, like poetry, essays, speeches, etc．His advice to us students is that for memorization purposes, there is forty minutes each day in which our memory is more acceptable than it is during the other 23 hours and 20 minutes.

    This 40-minute "super memory" period is divided into two parts: the 20 minutes before we sleep, and the 20 minutes after we first awake. The theory supporting this is pretty simple. First, the last information we input into our brain before bed has a better chance of taking root than information gained during the noisy daytime; and second, our mind is free of disturbance(干扰) when we first awake in the morning一so more receptive to inputs, like a blank slate（石板）．

    I took the advice to heart and it served me well in my school years. In my university days, our Chinese teacher would assign us 200 new vocabulary words each day, on which we would be quizzed（测试）the following day. Without the "magic" 40-minute technique, there's no way I would have passed those daily quizzes.

    As far as language study goes, it's not only useful for memorizing vocabulary. It's also a very useful window of time to listen to the language we're studying even with background noise, and even if it's at a level we find difficult to understand. It might be audio（声音的）language study, aids, or just radio, TV or whatever.

    Beyond our years of formal(正式的) education, memory skills are hugely important in any career. How many times have we heard a speaker read their speech from a prepared text, or read the word-by-word content of a PowerPoint presentation as they present each slide（投影片）? These are annoying, boring, and less effective ways of communicating. They are almost guaranteed(保证) to lose the audience's close attention and interest, let alone persuade or inspire anyone to do anything. And yet lots of people still make this mistake.

    If we use the 40-minute technique, we may not succeed in memorizing our presentation content on a 100% word-by-word basis, but we'll be familiar enough so that we can spend much more time making eye contact with our audience. We will get them in the process, while looking at our text instead of staring at it. This will also free up our hands and arms to convey some extra messages through gesture．

    As you see, the technique really works, but like many things, it takes practice to perfect it. Therefore, we'd better find ways to use the language outside of the classroom, as regularly and frequently as possible. One basic rule of language learning is, "Use it, or lose it·”

Seize the forty-minute learning window and we'll bring in a rich harvest of language learning.

Do you think you would work out more if you were offered money to do so? Science has shown that money can give people motivation to work out, but perhaps not in the way that you think.

According to a study published in the Annals of Internal Medicine Journal, the best strategy isn't offering money; it's giving someone money, then threatening to take it away.

Researchers gave 281 people the goal of walking 7,000 steps every day over 13 weeks.

To motivate the people who took part to reach the goal, researchers divided them into three groups.

People in the first group received $1.40(9 yuan) each day as long as they finished 7,000 steps, the second group was only able to collect the $1.40 if they had reached 7,000 steps the day before, and the third group was given $42 at the beginning of each month and $1.40 was taken away every time someone failed to meet the goal.

The third group met their daily fitness goals 50 percent more often than the other two groups, showing that people were most motivated to walk by the fear of losing money.

    “People are more motivated by losses than gains, and they like immediate gratification.” study author Dr Mitesh Patel, an assistant professor at the University of Pennsylvania in the US, told CNN. “They want to be rewarded today, not next year or far into the future.”

    Our brains tend to avoid wanting to lose things more than they try to get the benefits from gaining them, Patel explained. “It makes people think like the money is theirs to lose from day one.”

In addition, in most programs, many participants will drop out quickly and only the motivated will stay involved, Patel said.

    “In ours, we were pleasantly surprised that 96 percent stayed.” he added.

The study provides evidence that what matters is not only the money incentive （激励）, but also how you think about them. This is important to how effective they are. The evidence could have a big effect on health promotion programs in the future, according to the study.

“Incentives themselves are not all you need,” Stephanie Pronk, a health and wellness consultant with the Aonplc corporation, told The Wall Street Journal. “It's really important to change up the incentive design and keep people on their toes.”

    Leaving Hanoi on a fiercely hot summer day,after an hour by air,Luang Prabang gradually appears below our airplane wings.From a few hundred meters above,my first impression of this UNESCO-listed heritage（遗产）is an area of green land and mountains,surrounded by snaking rivers.

    Encircled by mountains,the former royal capital of Luang Prabang is more than just the country's picture-perfect showpiece.

    Travelers will be attracted to Luang Prabang by the city's timeless peacefulness with its shiny Buddhist temples, French colonial architecture and friendly people.

    Tourists visiting Luang Prabang shouldn't miss the chance to see one of the most sacred（神圣的）Lao traditions, tak bat,or the Buddhist almsgiving ritual（仪式）,which dates back to the 14th century.

    As the sun rises in Luang Prabang,hundreds of Buddhist monks depart from their temples to gather their daily offerings,which most commonly are rice,fresh fruit and traditional sweet snacks.The daily alms gathering begins on the main street before spreading to all the side streets.

    Our group of six got out of our comfy beds at 5 am to join other local residents and tourists to offer alms to the monks.We kneeled by the roadside in front of the 3 Nagas Hotel on the main street with big baskets of steamed sticky rice,waiting quietly until monks of all ages passed by to accept our gifts.

    The daily ritual gives you a wonderful opportunity to experience an ancient Lao tradition.However,there are some strict rules if you wish to join the event.

    Firstly,shoulders,chests and legs must be covered in modest clothing as a mark of respect.You should also remain a suitable distance from the monks.Photographs may be taken,but from a distance and never use a camera flash.The ritual has to be performed in silence.Talking to or touching the monks at any time,even when making an offering,is not allowed.

    Another must-do morning activity is to visit the local market,where you can see the generosity that Mother Nature offers this dreamy land.While walking through the morning market,located within a long and narrow hamlet,I was excited to see all kinds of products from the nearby river and jungle: some ill-fated squirrels lying next to fresh bamboo shoots,different kinds of wild mushrooms and vegetables displayed on banana leaves and giant river catfish in baskets.

    Although Luang Prabang is small,there are many things to see here.Active travelers can get up close and personal with Laos' gentle giants at the elephant conservation camp or take in some scenes of riverside life with a cruise or kayak excursion on the rivers.Two waterfalls that are perfect for picnicking in the foothills nearby,and classes are available in traditional crafts.

    China officially informed the World Trade Organization on Tuesday that it will ban the import of 24 different types of solid waste by the end of this year as part of a campaign to deal with environmental pollution and protect people's health.

    In response to growing public concerns over the potential environmental and health danger caused by the increasing amounts of solid waste imported into the country for recycling and treatment, China passed a special law in 1995 to control imports of waste materials, such as plastics, slag from steelmaking, unsorted scrap paper and discarded textile materials.

    A year later, the country published a list for solid waste imports and began implementing a permit system to control the import volumes and types of waste imported.

    However, due to the lack of effective supervision(监管) and the failure of relevant departments to fulfill their duties, solid waste imports have not been effectively controlled.

    So far, China is the world's largest importer of solid waste. According to the Ministry of Environmental Protection, China imported 7.3 million metric tons of plastic waste worth $3.7 billion in 2016, accounting for 56 percent of global imports of solid waste.

    Correct recycling of solid waste materials is an important part of the global economy, and moderate imports of scrap plastic, scrap paper and scrap rubber products, such as vehicle tires, can to some extent, make up for China's shortage of various raw materials.

    However, the lack of supervision has resulted in the country's severe soil and environmental worsening.

    Given that China's continuing efforts to push for industrial transformation and upgrading have resulted in a noticeable decline in the demand for the materials recycled from solid waste imports. It is right for the country to restrict such imports for the sake of the environment and public health, and to better adapt to the changed industrial structure.

    About three decades ago, China was known as the "Bicycle Kingdom". But later on, bikes were replaced by their fuel-powered competitors.

    But recent months have seen a recovery of the humble bike across China, with an increasing number of people choosing cycling instead of driving to schools, to workplaces or to do sightseeing. The introduction of bike-sharing schemes, pioneered by start-ups like Ofo and Mobike, has brought the trend to a new level.

    People can unlock the shared bikes by simply using their smartphone. The bikes are equipped with GPS and can be left anywhere in public for the next user. They're popular among many Chinese people as they provide an effective solution to the "last mile" problem, which refers to the final leg of a person's journey.

    " In places where the subway doesn't extend, where it's difficult to change from one kind of transport to another, it's so easy to get where you want to go with Mobike," Hu Hong,29,told AFP. She pedals(骑车)to her Shanghai real-estate job.

    However, the schemes have also led to problems such as illegal parking, vandalism(故意毁坏) and theft. Last month, two nurses in Beijing were placed under administrative punishment for five days for putting locks on two shared bikes. And in December, a man who stole a shared bike was sentenced to a 3-month detention(拘留),and fined 1 ,000 yuan by the Shanghai Minhang People's Court.

    " Bike-sharing is a greener method of transportation and provides a user-friendly experience,"said Liu Xiaoming, vice-minister of transport.

    " But it's a combination of online and offline business. Operators are usually strong in online services, but lack offline business experience, which causes problems."

    Now, Chinese service operators are trying to solve the problems. For example, a bike- sharing company called Mobike sets a 100-point credit score for each user, with points taken in the case of bad behavior. Once a score drops below 80, bike rental is increased to 100 yuan per 30 minutes, up from 0.5 - 1 yuan.