All too often, a choice that seems sustainable(可持续的)turns out on closer examination to be problematic. Probably the best example is the rush to produce ethanol(乙醇) for fuel from corn. Corn is a renewable resource —you can harvest it and grow more, almost limitlessly. So replacing gas with corn ethanol seems like a great idea. 

    One might get a bit more energy out of the ethanol than that used to make it, which could still make ethanol more sustainable than gas generally, but that's not the end of the problem. Using corn to make ethanol means less corn is left to feed animals and people, which drives up the cost of food. That result leads to turning the fallow land –including, in some cases, rain forest in places such as Brazil—into farmland, which in turn gives off lots of carbon dioxide (CO) into the air. Finally, over many years, the energy benefit from burning ethanol would make up for the forest loss. But by then, climate change would have progressed so far that it might not help.

    You cannot really declare any practice “sustainable” until you have done a complete life-cycle analysis of its environmental(环境的) costs. Even then, technology and public keep developing, and that development can lead to unforeseen and undesired results. The admirable goal of living sustainably requires plenty of thought on an ongoing basis.

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    Are you looking for a different place to visit this summer? Why not take a magical trip to an Earth-size planet beyond our solar system with NASA's Planet Travel Center?

    We live in a universe full of planets outside our solar system. Unluckily, even the nearest of those planets are light-years away, so sending spaceships and humans to these attracting worlds remains a distant dream. But on NASA's Planet Exploration website, you can start a journey on an imagined globe of a new world through 360-degree visualization（可视化）. As you land onto each globe's ground, you'll discover amazing views, like the blood-red sky of TRAPPIST-1d, or stand on a moon of the huge planet Kepler-16b, which appears larger than either of the planet's two suns. The view from each planet's ground is an artist's impression based on the limited information that is reachable; no real photos of these planets exist.

    The newest planet with such 360-degree visualization is Kepler-186f, an Earth-size planet rounding a star much cooler and redder than the Sun. “Kepler-186f is also so distant, and it is till now impossible to recognize their atmospheres—if they exist at all—or characterize their atmospheric qualities,” said Martin Still, scientist for NASA's newest space-based planet-hunting program, wondering people's reaction to their creation. “Though with such challenges unsettled, using the NASA visualization tool, you can see how the existence and disappearing of an atmosphere would change the view of the sky from the planet's ground.” Still added.

    Aaron, head of Planet Travel Center, points out that their present and future schedules of the globe visualization will find the nearest planets to our solar system and characterize their atmospheres, bridging the gap between our imagination and what's really out there. In the near future, all the 360-degree visualizations are viewable on desktop and mobile devices, like smartphones, allowing all readers a wonderful enjoyment from the possibilities of a new world.

    A team of researchers at the University of Illinois at Chicago found that too many kids are eating too much pizza and too many calories are doing harm to children's health.

    "There are a lot of takeaways from the study. But the biggest thing is that parents are serving their kids too much pizza," said Dr. William Dietz, one of the study's authors and the director of the Sumner M. Redstone Global Center for Prevention and Wellness at the Milken Institute of Public Health at the George Washington University.

    The researchers used data from the National Health and Nutrition Examination Survey, which tracked the diets of more than 11,000 children and teenagers. Researchers figured how many children eat pizza in the United States, how often they eat it, and how much they eat when they do.

    Pizza, pretty alarmingly, is the second leading source of calories in the diets of America's children, next only to grain desserts, such as cookies and other sweets. On any given day, roughly 20 percent of all children aged 2 to 11 and adolescents aged 12 to 19 eat pizza. And when they do, they eat a lot of it. When children eat pizza, they eat roughly 400 calories, according to the study. For teenagers, it's upwards of 600 calories.

    All that is pretty problematic, according to Dietz largely because kids don't tend to balance the pizza slices with salads, vegetables and other more nutritional(有营养的) foodstuffs. Days on which children and teenagers eat pizza are not only associated with considerably higher intakes of fat, but also, quite simply, with more food: on average, children consume 84 extra calories on the days they eat pizza, while adolescents consume an extra 230 calories.

    "When you eat extra calories and don't compensate(抵偿) for them at another point of the day or week, it can lead to weight gain and even obesity." Dietz said.

    There is a Silver lining. Pizza consumption is still too high by nutrition standards, but it's lower than it used to be. Consumption(消费) fell by roughly 25 percent between 2007 and 2016, according to the study. Much of that has come at dinner where it's fallen by 40 percent for children and about 33 percent for teenagers. It's unclear whether the decline has been in connection with a growing concern over obesity, especially among the country's youth.

    But the drop in pizza consumption, while significant hasn't been big enough "It's a positive trend," Dietz said. "But we're not quite them yet."

    It's easy to see the appeal of pizza. It's cheap. Parents can buy a lot of pizza for not a lot of money. Besides, they can buy pizza from a chain shop, a mom-and-pop store or a grocery freezer. And it's universally loved. The estimated 3 billion pizza eaten each year in the United States is a proof of the food's unmatched popularity. Given how much the country loves pizza, what's to be done? Dietz suggests pizza with smaller serving sizes and healthier toppings(配料). "We're not suggesting that kids avoid pizza altogether." said Dietz. "But when parents serve it, it's important that they understand it's extremely caloric. They should serve smaller pizza, or at least smaller slices."

    The British live on a small island. They are surrounded by the sea, so it is not surprising that the sea has always played an important role in their lives. After the development of large, ocean­going sailing ships in the fifteenth century, the sea became even more important to the country's development. Ships setting sail from England determined to extend Britain's territories, its wealth and its knowledge of the world. Ships returned to England bringing goods, people and new ideas from foreign places. By the nineteenth century, Britain had the largest, most powerful navy in the world.

    The great sailing ships were so much a part of British life that they even affected the language. Many English expressions we use today were originally nautical (航海的) terms, although most people no longer realize this. For example, people commonly describe an honest and fair business deal as being "above board". This expression was originally used in sailing ship times when secretive, dishonest ship's business would be carried out below decks (below the boards) out of public view. On the other hand, honest business was always conducted on deck (above the boards), in the open where everyone could see what was going on.

    "Pipe down!", meaning "Be quiet!", is another common expression that has nautical origins. The ship's boatswain (水手长) would blow a whistle, or pipe, at the end of the day to indicate (表明) to the sailors it was time to quieten down and go to sleep.

    Most native English speakers have heard the expression "not enough room to swing a cat", but few know that the "cat" does not refer to a small furry animal with four legs and a tail. The "cat" is actually a short form of "cat of nine tails" — a whip with nine, knotted (打结的) tails. A boatswain needed a lot of space in order to swing the whip properly when lashing (鞭打) a poor sailor under his control!

    If you want to disturb the car industry, you'd better have a few billion dollars: Mom-and-pop carmakers are unlikely to beat the biggest car companies. But in agriculture, small farmers can get the best of the major players. By connecting directly with customers, and by responding quickly to changes in the markets as well as in the ecosystems(生态系统), small farmers can keep one step ahead of the big guys. As the co-founder of the National Young Farmers Coalition (NYFC, 美国青年农会) and a family farmer myself, I have a front-row seat to the innovations among small farmers that are transforming the industry.

    For example, take the Quick Cut Greens Harvester, a tool developed just a couple of years ago by a young farmer, Jonathan Dysinger, in Tennessee, with a small loan from a local Slow Money group. It enables small-scale farmers to harvest 175 pounds of green vegetables per hour—a huge improvement over harvesting just a few dozen pounds by hand—suddenly making it possible for the little guys to compete with large farms of California. Before the tool came out, small farmers couldn't touch the price per pound offered by California farms. But now, with the combination of a better price point and a generally fresher product, they can stay in business.

    The sustainable success of small farmers, though, won't happen without fundamental changes to the industry. One crucial factor is secure access to land. Competition from investors, developers, and established large farmers makes owning one's own land unattainable for many new farmers. From 2004 to 2013, agricultural land values doubled, and they continue to rise in many regions.

    Another challenge for more than a million of the most qualified farm workers and managers is a non-existent path to citizenship — the greatest barrier to building a farm of their own. With farmers over the age of 65 outnumbering(多于) farmers younger than 35 by six to one, and with two-thirds of the nation's farmland in need of a new farmer, we must clear the path for talented people willing to grow the nation's food.

    There are solutions that could light a path toward a more sustainable and fair farm economy, but farmers can't clumsily put them together before us. We at the NYFC need broad support as we urge Congress to increase farmland conservation, as we push for immigration reform, and as we seek policies that will ensure the success of a diverse and ambitious next generation of farmers from all backgrounds. With a new farm bill to be debated in Congress, consumers must take a stand with young farmers.

    Back in 1988, I was working at the University of Bonn in Germany as a research fellow. I took some time off in early May to visit a friend, who was the director of a museum in Viterbo, in central Italy. I set out by train, which crossed the Swiss border to reach Zurich, winding through valleys and along hillsides, and entering tunnels and making its way through the Swiss Alps. The scenery was so beautiful.

    The train then crossed the Italian border before passing through Milan and Florence, then finally stopping in Rome. I was lucky, as my hotel was close to the railway station. The next morning, I had a coffee at a nearby café and eagerly set out to visit as many of the famous Roman landmarks as possible.

    The following day I headed back to the train station, intending to take a short train ride to Viterbo to meet up with my friend. When I arrived at the station and attempted to locate the correct platform, I quickly realized that the station was closed for an upgrade (升级). For a moment my mind went blank and did not know what to do. My biggest problem was my luggage—my suitcase and hand luggage were so heavy that I couldn't move about easily. As I don't speak Italian, I could not ask anyone for instructions. I dragged my suitcase about 100 meters to a nearby motor mechanics. A tall, strong man of about 50 years of age was working there and I excused myself and asked where the nearest station was. I am sure that he did not understand me properly but he could easily guess that I was looking for a station. He replied, but I did not understand.

    He smiled, wiped his hands and said something, which I guessed to mean "come along". So I dragged my suitcase along and followed him. He opened the door of his car, motioned to me to get in and then drove for a few minutes to the next station. I got out, unloaded my luggage, then shook his hand with thanks. He smiled back and drove away.

    There was no time to hug or exchange names  I understood he was busy and in the middle of his work. I was moved so much by his generosity that I have never forgotten him.