People often ask which is the most difficult language to learn, and it is not easy to answer because there are many factors to take into consideration. Firstly, in a first language the differences are unimportant as people learn their mother tongue naturally, so the question of how hard a language is to learn is only relevant when learning a second language.

    A native speaker of Spanish, for example, will find Portuguese much easier to learn than a native speaker of Chinese, for example, because Portuguese is very similar to Spanish, while Chinese is very different, so first language can affect learning a second language. The greater the differences between the second language and our first, the harder it will be for most people to learn.

    Many people answer that Chinese is the hardest language to learn, possibly influenced by the thought of learning the Chinese writing system, and the pronunciation of Chinese does appear to be very difficult for many foreign learners. However, for Japanese speakers, who already use Chinese characters in their own language, learning writing will be less difficult than for speakers of languages using the Roman alphabet.

    Different cultures and individuals will find different languages more difficult. In the case of Hungarian for British learners, it is not a question of the writing system, which uses a similar alphabet, but the grammatical complexity, though native speakers may find it easier, struggling with languages that the British find relatively hard.

    No language is easy to learn well, though languages which are related to our first language are easier. Learning a completely different writing system is a huge challenge, but that does not necessarily make a language more difficult than another. In the end, it is impossible to say that one language that is the most difficult language in the world.

    As free as they make us, mobile phones still need to stay close to a power source. Soon that may change with "green" power.

    Three Chilean students got the idea for a plant-powered device(装置) to charge their cellphones, while sitting in their school's outdoor courtyard during a break from exams, with dead mobile phones. Then, one of them had an "aha" moment.

    “It occurred to Camila to say about plants,” said inventor Evelyn Aravena. “'Why don't you have a socket, if there are so many plants? 'After that, we thought, 'why don't they have a charging outlet? Because there are so many plants and living things that have the potential to produce energy, why not?'”

    Their invention—a small biological circuit called E-Kaia—uses the energy plants to produce during photosynthesis(光合作用). A plant uses only a small part of that energy and the rest goes into the soil, and that's where the E-Kaia collects it. The device plugs into the ground and then into your phone.

    "It's the most amazing project I've ever seen in my life, plain and simple. They brought this original model, and it worked — and that's when it all changed, at least from my personal point of view and I began to support them." said Mauricio Cifuentes.

    The device solved two problems for the engineering students — they needed an idea for a class project, and an outlet to plug in their phones.

    "Looking for a place to charge the notebook, which had no power, and the mobile phones, we weren't able to find anything because all the other students were in the same state of madness trying to find a place to charge their devices," said Aravena.

    But plants are everywhere, and the bio－circuit makes the best of their excess(过多的) power.

    The E-Kaia doesn't carry much charge but it's powerful enough to completely recharge a mobile phone in less than two hours.

    The student inventors have applied for patents on their technology, and expect the E-Kaia to go on sale in December 2016.

    The Taj Mahal (泰姬陵) is a love story, a sad and beautiful one. If it didn't exist, we would easily imagine that the story of its construction was simply a fairy tale. Three hundred years ago, there lived an Indian emperor called Shah Jahan. His wife was a beautiful and bright woman whom he loved greatly. Her title was Mumtazl Mahan: its shortened form Taj Mahan means "pride of the palace". In the year 1630 this beloved wife of the emperor died. He was so brokenhearted that he thought of giving up his throne. He decided out of his love for his wife, to build her the most beautiful tomb that had ever been seen.

    He summoned the best artists and architects from India, Turkey, Persia and Arabia and finally, the design was complete. It took more than twenty thousand men working over a period of 18 years to build the Taj Mahan, one of the most beautiful buildings in the world. The building itself stands on a marble platform 29 meters square and 67 meters high. Towers rise from each of the four corners. The Taj itself soars another 61 meters into the air. It is an eight-sided building made of white marble. The emperor planned to build an identical tomb of black marble for himself on the other side of the river connected by a silver bridge. However his son put him into a prison in the palace before he could finish, and for the rest of his life, he could only gaze across river at the tomb of his beloved wife.

    Microsoft PowerPoint is the world's most common presentation tool. It emerged from software company Forethought Inc in the 1980s. Bob Gaskins was the man behind it.

    "I knew in the early 80s that there were as many as a billion, a thousand million presentation slides being made per year just in America," Gaskins says, but they were all made by hand and almost nobody was using computers to do them.

    "It was clear to me that here was a huge application worth billions and billions of dollars a year that could be done on computers as soon as there was a revolution in the kinds of computers that we had."

    Gaskins was onto something, but it was a hard sell at the time. The software wouldn't run on any existing personal computers. Anyone wanting to use it had to buy a new machine. Even so, people bought personal computers for the first time in order to be able to use PowerPoint, says Wired magazine journalist Russell Davies.

    Davies explains that before PowerPoint, people used slides to convey information to groups — but anyone creating a presentation had to send away to get their materials made. It took a long time to do, was difficult to make changes and because it was so expensive, only the most senior people in an organisation got to do it.

    "PowerPoint," Davies says, "made it possible for everyone in an organisation to stand up and say their piece."

    PowerPoint has helped turn us all into presenters — but it' s also been accused of over-simplifying ideas and distracting (干扰)us from clear thinking.

    Sarah Kaplan is a management professor at the University of Toronto's Rotman School of Management. She has noticed that, rather than people asking for new analysis or insights in meetings, they were asking for more PowerPoint slides.

    Kaplan says that some CEOS, such as Amazon's Jeff Bezos, have banned its use. "He felt, and I think many people feel, that PowerPoint became such an object of the process that they lost the ideas inside of it and that is the risk."

    Ancient Chinese folk paintings and many other art styles have been passed down from generation to generation, and are still practised in different parts of China. Here's a look at four unique Chinese folk art forms.

    Chinese Opera (戏剧) is the traditional form of Chinese drama. According to incomplete statistics, in China's various ethnic regions there are about more than 360 kinds of operas. The most famous ones include Peking Opera, Kunqu Opera, Yueju Opera, Yuju Opera, Sichuan Opera, Fujian Opera, Hebei opera, Huangmei Opera arid so on, in total more than 50, among which Peking Opera is the most popular in China.

    Shadow Play (皮影戏) dates back to Western Han Dynasty in Shaanxi more than 1,000 years ago. The moving figures, usually carved out from leather, are operated by folk artists, accompanied by music and singing. It is the world's first dubbed (配音的) motion picture art form, thus considered the "ancestor" of modern film. Today this art form is still popular in northern China.

    Paper-cutting (剪纸) is one of the most popular traditional decorative arts in China with a long history. Paper-cutting can be seen across China and it has even developed into different local genres (流派). They are usually used to decorate gates and windows during festivals.

    The Kite was invented by Chinese people. According to legend the earliest kite in China was a wooden bird by Mo Di in the Eastern Zhou Dynasty. Later his student Lu Ban improved the tech and used bamboo as material to make a kite. Today, various kite-flying activities can be found in different regions of China. Shandong Weifang Kite Festival is held every year and attracts lots of kite lovers and travelers.

    Mom wanted only one thing for her birthday. "Can you find me another copy of this song?" she asked, and handed me a worn-out cassette tape. I knew exactly what was recorded on it: My Redeemer. I heard the song played at least a thousand times while growing up. After so many years, the cassette tape was too worn out to be used. I promised her I would find a replacement.

    My Redeemer became Mom's favorite song after my younger brother Tim was killed by a drunk driver in 1973. The only thing that helped her calm down was the soulful sound of My Redeemer from the local radio station. We recorded it on a cassette tape so she could listen to it any time she wanted but none of us knew who the soloist(独唱者) was. These days, I thought the song would be easy to find out. I went home and searched the Internet. Several songs with that title popped up, but none of them was the one Mom loved. I got frustrated.

    Mom's birthday drew near and then one day, I was driving home, listening to our local radio station. A familiar tune came on. It was My Redeemer!As soon as I could, I phoned the station. I got a line on the soloist, who was called Alan Parks. I typed his name into Google and found his home number in South Carolina. Minutes later, I was telling him how much his recording meant to Mom. He offered to ship two CDs out to me personally. I gave him my address. "Red Lion, Pennsylvania?"he said. "Do you know the Logans?""They are our neighbors!""I've been friends with them for 25years," Alan said. "They'll be at my concert at York Gospel Chapel on April 17th. Would you and your mom come too?" We sure would. Mom was excited to hear Alan sing My Redeemer to her, live in concert-on the evening of her 87th birthday.