Scientists are debating how to limit their newly-discovered power to change genetic structure (结构). Scientists already modify the genes (基因) of farm animals and agricultural plants to make them more productive or stronger. But now they can also change genes in wild animals and plants. These genes would continue into later generations. For example, it may be possible for scientists to remove from existence the kind of mosquitoes, small flying insects, that carry the Zika virus. They might also be able to permanently remove species (物种) of plants and animals that are damaging to other species.

    In a report published last week, the U. S. National Academies of Sciences, Engineering and Medicine (NAS) said it supports continued research on this kind of gene control. But it warned that it is not possible to know what will happen when these changed plants and animals are released (释放) into the wild.

    Sixteen biologists, ethicists (伦理学家) and policymakers are on an NAS committee that is examining the issue. They say that there is value to the new technology. But, they say, there is not enough evidence to support the release of modified organisms (生物体) from the laboratory into nature.

    Many people would support stopping mosquitoes and rats from carrying diseases. But scientists say we must understand the possible scientific, ethical, legal and social results of such action before we decide whether to take it. Gene modification is spread through reproduction (繁殖).

    Changed genes will continue to spread as long as an animal or plant continues to reproduce. They cannot be limited to a farm or kept within a country's borders. Scientists are wondering what may happen if a modified organism mates with another species. They are not yet sure how the modified genes would affect the other species. It is possible that those genes could harm those creatures or even lead to their disappearance from our planet.

    The English writer Samuel Johnson famously said, “You find no man who is willing to leave London. No, sir, when a man is tired of London, he is tired of life, for there is in London all that life can afford.” More than two centuries have passed since Johnson's age, but his words still ring true. Here, you'll find the historic Tower of London and the Tate Modern both considered must-sees. Shakespeare's sonnets（十四行诗） are still being uttered by actors. Londoners most certainly still look up to the royals, but they also rock out to Coldplay and Lily Allen. And while they still sip tea, they now drink Starbucks, too.

How to Save Money in London

    Find the free attractions. Many of London's top things to do, including the National Gallery, Hyde Park and the Portobello Road Market, are absolutely free to enjoy.

    Ride the Tube. Taking taxis will add up quickly, so buy a pay-as-you-go Oyster Card and travel on London's underground system, nicknamed the “Tube”.

    Dine smart. Corridors like Brick Lane offer fantastic cultural food for bargain prices; fish and chip shops are a cheap standby and takeaway food costs less than dine-in.

London Culture & Customs

    London is one of the fashion capitals of the world, and its residents tend to reflect that. Practically, pack an umbrella for the rainy days and a scarf for the cold ones. As for tipping, restaurants and cafes will usually add a 10-to-15-percent service charge to the bill. If a service charge is not allotted（指定）, it's customary to tip the same (between 10 and 15 percent). If you're drinking at a pub or wine bar, tipping is flexible. And in a taxicab, tip the driver to the nearest pound or about 10 percent of the cost.

London Dining

    London used to be highly criticized for its heavy and common menu items. Now, London is considered as one of the most gourmet cities in the world. And with its melting pot of cultures, it's not difficult to see why. London offers everything from modern British to Malaysian. For Indian food, we suggest visiting the curry houses on Brick Lane. If you want a real high tea experience, book reservations at the Ritz, at Fortnum & Mason, or at the Dorchester — but be sure to dress the part. Pub culture is still alive and well, so if you have a hankering for fried fish and salty chips (or French fries), you'll still find them here. And for a quick bite, exchange a few pounds for a kebab, a quick sandwich or some to go sushi, which can be found in restaurants throughout the city.

    Even if trees cannot walk, they are still on the move.

    In parts of the Arctic, entire forests are moving northward. Across the Arctic, temperatures are rising faster than anywhere else in the world. As that happens, the tree line that marks where forests stop and the treeless tundra(冻土地带) starts has been shifting northward. Trees growing along the tree line must protect themselves from the cold wind. To do this, plants tend to grow horizontal(水平的) branches low to the ground. The energy it takes for trees to grow this way means they don't have enough energy to make seeds.

    But as Earth's climate has been warming, trees no longer have to just grow horizontally. Many can instead grow up toward the sky. This takes less energy. And with all the leftover energy. these trees have started producing more seeds. This happens especially in places where the white spruce(白云杉) grows.

    White spruce, which is a North American tree, is quite able to produce a lot of seeds, which can move long distances in the wind. When wind-blown seeds end up on the tundra beyond the tree line, they eventually can sprout(发芽) new trees. This explains how a forest can move. Of course, the process would work only if the tundra were warm enough. But in recent years, the whole planet has been warming.

    New trees will provide shelters for some snow, keeping the sun's rays from making the white surface disappear. Instead, the trees absorb the sun's heat. This warms the surrounding air. The extra warmth encourages even more trees to produce seeds. That further boosts a forest's ability to expand. In addition, more trees will trap more snow, preventing much of it from being blown away. Snow can trap heat in the soil below, which encourages trees to grow. The recent rise of temperature has helped more trees grow. The recent rise of temperatures has helped more trees grow past the tree line. People worry about impacts on the animals that depend on frozen conditions for food and shelter.

    A British friend told me he couldn't understand why Chinese people love eating sunflower seeds as a snack so much. “I've met a lot of older Chinese and many have a crack in their front teeth; I believe that's from cracking the seeds, ” he said.

    I had never noticed the habit, but once he mentioned it, I suddenly became more aware. I realized that whenever I'm watching TV or typing a report, I always start mindlessly cracking sunflower seeds. My friend doesn't like sunflower seeds, and, to him, it seems unnecessary to work so much just to get one small seed.

    When we were young, the whole family would usually get together for Chinese New Year. Then, we all lived close to one another, usually in a small city, and sometimes even neighbors would go door-to-door on Chinese New Year's Eve to check out what every household was making.

    I remember my parents would be in the kitchen cooking. Out in the living room , a large table would already be laid out, complete with fancy tablecloth, ready-made dumpling fillings, and dishes full of candy, fruits and sunflower seeds. Some of the dishes were to be offered to our ancestors later, while others were for neighbors and children to eat before the evening feast. I must have learned how to crack sunflower seeds back then.

    I don't think it's right to criticize one's choice in food or eating habits, no matter how strange they may seem.

    It's not only in China. When I went abroad, I found people had all sorts of strange habits when it came to food. In Denmark, they put salted red fish on bread and eat it for dinner, no matter how much it ruins your breath. They think it's a delicacy, and it's connected to their culture. I think it's a wonderful tradition.

    In today's world of smart phones and laptops, most people have at least one time-telling thing with them. Since these digital products are so common, is time running out for the 500-year-old watch? According to some consumers, the answer is yes. New Jersey teenager Charlie Wollman says a watch is “an extra piece of equipment with no necessary function.” Many young adults think so and use their smart phones to tell time. It is said that fewer young people wear watches today than ten years ago. As a result, some people say that the watch industry is at a crossroads.

    However, watchmakers optimistically say that watches redeem（挽回）popularity when consumers reach their 20s and 30s. By then, they are willing to spend money on a quality watch that doesn't just keep good time. Fifty years ago, watchmakers took pride in their products' accuracy（精确性）. But in recent years, the watch industry has changed itself into an accessory(配饰) business. And today, the image a watch conveys has become more important than the time it tells.

    "Complications" features that go beyond simple timekeeping — are an important part of a watch's image. Today's watches offer lots of features that meet almost any personality. These features include compasses, USB drivers, and even other functions that measure the effectiveness of golf swings!

    Creativity also plays a key role in designing today's watches. For example, Japanese watchmaker Tokyoflash makes watches that don't even look like watches. The company's popular Shinshoku model uses different color lights to tell time. It looks more like a fashionable bracelet than a watch.

    Whether a watch conveys fashion sense, creative talent or a love of sports, consumers want their watches to stand out. Nowadays, everyone has the same kind of gadget（小玩意） in their bags, so people want to make a statement with what's on their wrists. Will this interest in wrist fashion last? Only time will tell!

    Are your eyes irritated, dry, watery, blurry, seeing double or sensitive to light, and do your back and neck ache? If so, you are likely one of many people today who suffer from digital eyestrain, also called computer-vision syndrome.

    Eyestrain is often related to the amount of exposure to screens, the distance from eyes to screens and the use of multiple screens simultaneously. However, studies have also shown that the blue light produced by digital devices today reaches further into the eyes than other kinds of light. This light actually assists attention during the day but can result in interrupted sleep patterns at night.

    Scientists have also said that eyestrain is not a necessary evil, even in a modern world that revolves around technology. Changing some simple details about your relative position to screens, such as staying about 60 centimeters away, will help. Also, avoid overhead and other direct sources of light, and use shaded lamps and window blinds while looking at digital devices instead.

    Beyond the way that relates to digital screens, there are also ways to change how you view screens that are helpful in combating eyestrain. To begin with, your computer screen should be high-resolution(高清的), at least 50 centimeters wide diagonally and may require a screen filter to decrease reflections. Also, be aware that "computer glasses", which cut down glare and blue light, are available and those contact lenses can increase the risk of eyestrain.

    Besides, to reduce your risk for computer-vision syndrome and neck, back and shoulder pain, take frequent breaks during your computer workday. Many workers take only two 15-minute breaks from their computer throughout their day. According to a recent study, discomfort and eyestrain are significantly reduced when computer workers take four additional five-minute "mini-breaks" throughout their workday. And these additional breaks don't reduce the workers' productivity.

    Finally, many of us fall into bad habits while using digital screens that only worsen the effects of eyestrain. While viewing digital screens, many people blink one third less often than they usually do. Place a reminder on your computer to "blink" so that your eyes don't dry out. Also, rest your eyes' focusing muscles by using the 20-20-20 rule: Every 20 minutes, focus on something 20 feet away for 20 seconds.