People who do not get enough vitamin A in their diet may develop night blindness. But in the developing world, a lack of vitamin A causes much more serious harm to children. The world Health Organization links the lack of vitamin A to as many as 250,000 child deaths every year.

    One excellent source of vitamin A is found in newly developed sweet potatoes with orange flesh. Orange sweet potatoes contain high levels of beta-carotene, which the body changes into vitamin A. Experts say orange sweet potatoes could help the Africans who are lacking in vitamin A. But, first, more people will need to be persuaded to eat them. Sweet potatoes need a better image in Africa. Jan Low with the International Potato Center says, “We do have an image problem with sweet potatoes. In many African countries, they are seen as a crop of the poor.”

    Ms. Low explains that sweet potatoes are mainly grown by poor women to feed their families in case another crop fails. The sweet potatoes commonly grown in Africa have white or yellow flesh. But they are low in vitamin A.

    Jan Low took part in a project to study how to market orange sweet potatoes to Africans best. She worked on an information campaign(活动) in Mozambique and Uganda. The campaign included radio messages about the nutritional(营养的) benefits of the orange sweet potato. They advertised its ability to “fight diseases, make you strong, clear you skin and make you look healthy”. In areas without radio, the campaigners spread the message through theater. The performances included singing, dancing and storytelling. And everywhere they went, the campaigners wore orange T-shirts and hats. They even drove orange cars.

    Dan Gustafson heads the Washington office of the United Nations Food and Agriculture Organization. He mentions the efforts in the past to increase the popularity of other nutritious crops. He says most of these efforts failed because organizers of the campaigns did not consider what people wanted to eat. People want to eat what they are familiar with. But Mr. Gustafson sees a better chance for the efforts to increase the popularity of the orange sweet potato in Africa. Except for the color, the orange sweet potato is almost the same as what people already eat. Dan Gustafson says, “I think this time the campaigners will succeed, because they have made enough advertisements and the difference between the vegetable they have advertised and what people already eat is not a radical one.”

    To the people who came to Christopher Morley Park in Roslyn, he had no name. To them, he was “the ice cream man”. He was just two hands and a smile handing back ice cream from the van（面包车）window. To me, he was my older brother, Andrew.

    Once, he worked on Wall Street. But later he spent his days selling ice cream to an endless line of kids, moms and dads in swimming suits, perhaps daydreaming of a beach faraway.

    All day long, while he sold bags of potato chips, cans of soda, and all types of ice cream, he would do this sort of robotic motion—turn to the right, stoop down, hand the item out of the window and collect the money.

    His drinking days were over now. They neared their end one night after he took a severe beating when someone followed him home and robbed him when he was drunk. It left him memories of pain and misery. He was determined he would never take another drink again.

    One day years later, I went to look for him. I slipped into the high driver's seat and sat quietly watching him work. Occasionally, he would ask me to hand him a diet root beer or a bag of chips for sale, all the time bending over as he worked the long line.

    As I watched him sell ice cream from a van window, he taught me something about living this life that we all pass through too quickly. It was a lesson about trying to live it with grace and dignity and style, no matter what.

    He died in March 1999. He had served in the Army for two years in Europe in the 1950s. They gave him a soldier's funeral with a folded flag.

    India has many festivals, with some celebrations that last for weeks. However, none of them come even close to Holi, India's most colorful and fun festival. Celebrated on the day following the full moon, this year's festival happens to be on March 19th.

    As with most Indian festivals, this one also has many different folk stories. Most of them center around the success of good over evil. The most popular one is about a king, who hates his son Prahlada for loving the creator of the Universe－Lord Vishnu. When every attempt to stop him fails, his sister, Holika believed to be immune (免疫的) to fire, joins in the effort by inviting the young boy to sit with her inside a huge fire. Helped by the power of Lord Vishnu, Prahlada escapes safely, while the evil Holika is burned to death. To remember this event, huge outdoor fires are lit in the night before Holi in order to clean the air of evil spirits and to celebrate the death of the evil.

    So what's so great about this day? While there are some fun parades (游行) and folk songs and dance performances, the most fun of all is walking to the streets and splashing (泼洒) people with water guns and dry colors and even covering them with entire buckets of colored water. On this day, everybody is fair game, no matter how old or how young.

    At about midday, the splashing comes to an end and people living close to oceans or rivers usually take a bath in the water to clean themselves before going home to a delicious home­made big dinner and a well­deserved short sleep, following this full day of fun and activities.

    Turning the lights out or wearing a blindfold while eating could be a quick way to lose weight, according to scientists. The simple trick works because it stops diners eating for pleasure rather than for calories. It also triggers (引发) a part of the brain that is worried that unseen food may go bad.

    An experiment by the University of Konstanz, in Germany, found that people who were blindfolded consumed nine percent fewer calories before they felt full, compared to those who could see. They also vastly overestimated how much they had eaten because they could not see how much was left on the plate. Blindfolded volunteers estimated(估计) they had eaten 88 percent more than they actually had.

    Scientists believe that not seeing food on the table also allows the body to know when it is full in real time rather than remembering past experiences where it might have taken a full plate to feel full.

    In the experiment, 50 people were blindfolded and 40 were allowed to see their food. All were told not to eat within two hours of the experiment. They were then given three 95g bowls of chocolate ice cream and invited to eat for 15 minutes. Their bowls were taken away and the remaining ice-cream weighed, while the participants were quizzed on how much they thought they had eaten.

    On average the group who could see ate 116g while the blindfolded groups ate 105g. However, the blindfolded group believed they had eaten 197g while compared with 159g for the non-blind volunteers. They were also asked how pleasant the ice-cream tasted and the blindfolded group rated lower than those who could see.

    “The experienced pleasure of eating was significantly lower in the blindfolded group. Not seeing the food might have decreased the appetite. Sight plays an important role in the eating experience and in the overall dining experience.”

    Previous studies have shown that the visual influence of food plays a large part in the taste. While restaurants that allow diners to eat in the dark state that it triggers other senses, in fact eating in darkness is likely to taste far milder than usual.

    Some of the world's biggest companies—Apple, Amazon, Facebook—didn't exist 30 years ago. So what firms are we working for in 2050? That's a question put forward by historian Yuval Noah Harari in his new book "21 Lessons for the 21st Century".

    He argues that because technology is changing so fast, it's one of the first times in human history when we don't know what jobs will look like in the coming three decades." So the best bet is to focus on emotional intelligence（EQ）," he said. "Information is the last thing the kids need. They have too much of it."

    In this book, he focuses on the various challenges facing us today. As he writes in the book's introduction: "What are today's greatest challenges? What should we pay attention to? What should we teach our kids?" One area where these questions crop up is artificial intelligence（AI）Harari believes that AI will completely affect the job market for the next generation of workers.

    His first two books—"Sapiens" and "Homo Deus"—became international bestsellers, selling more than 12 million copies worldwide. They were praised by the likes of Mark Zuckerberg, Barack Obama and Bill Gates. Harari's books, about the past and future of humanity, attract a great number of fans. Fellow Israeli, actress Natalie Portman, is a fan. So is American R&B star Janelle Monae.

    As for Bill Gates, he might be Harari's biggest fan. So when the New York Times asked him to review Harari's latest books, he jumped at the opportunity. "All the three books wrestle with some version of the same question: What will give our lives meaning in the decades and centuries ahead?" Gates wrote in his review. "So far, human history has been driven by a desire to live longer, healthier, happier lives. If science is eventually able to give that dream to most people, and large numbers of people no longer need to work, what reason will we have to get up in the morning?"

    Volunteering abroad is a great way to help others, improve your skills and become a more confident, independent person. If you are interested in volunteering abroad, here are some places to go.

    Australia

    If you seek a life on the beach, in a great climate with friendly people, Australia might be your best bet. With thousands of volunteers already signing up to leave for Australia during the holidays, it will be a very popular option.

    Brazil

    This vast country has some great opportunities on offer and is especially popular this year. A lot of volunteer work is available in Brazil centers on conservation and ecological projects. With the world's largest rainforest in Brazil, of which huge part is in danger, there are lots of different jobs you can do.

    Kenya

    Kenya is the destination for those seeking an African experience. Generally volunteers in Kenya work in orphanages (孤儿院) or with local children living in slums (贫民窟). There is a great demand for volunteers in Africa because many people live in poverty, so if you truly feel like making a difference to a community, Kenya should be at the top of your list.

    Costa Rica

    Golden sandy beaches, clear coastlines and beautiful cities are what Costa Rica is all about. Because of its small size, you can see a lot of the country in just a short time. You can really make the most of your time as a volunteer. A lot of work is needed with wildlife and ecological work, so if you want to look after turtles (海龟) on the beach, Costa Rica could be just the place for you.