Campers Gene and Marie Marsden took pride in being good citizens when in the wild. While driving miles to the Green River Lakes area, they taught their children what they had learned in the bear safety handbook put out by the Bridger-Teton Forest Service.

    Mr. and Mrs. Marsden did their best to keep a tidy camp. As the handbook had said to hang all food at least ten feet off the ground and four feet out from the trees, they did that and locked their food in their trailer(拖车) at night. It was already dark when they went to bed, but they perused the campsite with flashlights, making sure nothing was left out. Following the bear book's advice, they slept a hundred yards from where they cooked their food, and kept the car near their tents, separated from the trailer, which they left up at the other camp.

    The Marsdens liked having their dog Spike on guard. But on the first night, Spike would not stop barking. When Marie Marsden pulled the tent open and shone her flashlight, she saw a young bear.

    They all piled into the car and drove quickly down the path, calling out of the window to Spike and abandoning the trailer. They drove to a pay phone and called a Fish and Game Department guard, who identified the bear by the white ring of the fur the Marsdens had seen around his neck. The authorities informed the Marsdens that the bear was a young male that they'd been keeping an eye on.

    The next morning, the Marsdens heard helicopters circling over the mountain and wondered if it might have something to do with the bear.

    After spending the night in the public campground, they drove back to their site. Wandering the area in search of clues, Marie came to a stop below a tall tree. She slapped her head and shouted, “Oh no!”

    “What is it?” Gene asked.

    Marie pointed at the ground where Spike's dog food bowl lay upside down. A week after their return home, the Marsdens read the headline in their local paper. “Bear Killed in Wind Rivers.” According to the article, the Fish and Game Department had shot the young bear because, having been rewarded for invading(侵入) a human campsite, it would likely to do so again.

    The Marsdens knew they had been lucky in the encounter, yet much to their shame and sadness, they also knew that the bear had not.

    Researchers in China and the United States have developed a new cataract(白内障)treatment with cells that has restored vision in babies in a trial and may eventually be used in adults.

    The treatment- by doctors and staff members at the University of California, San Diego School of Medicine and Sichuan and Sun Yat-sen universities in China-was published in March 9 edition of the scientific journal Nature.

    A cataract is a clouding of the normally clear lens(晶体)of an eye. Typical cataract operation involves the removal of the cloudy lens and the insertion of an artificial one. The new operation has been tested in animals and during a small, human trial. It resulted in fewer complications(并发症)than the current harmful operation, and in regrown lenses with superior visual function in all 12 of the baby cataract patients who received the procedure.

    A congenital cataract- lens clouding that occurs at birth or shortly after- is important cause of blindness in children. In the new research, Kand Zhang, head of ophthalmic genetics at US San Diego's Shiley Eye Institute, and his colleagues relied on the regrown potential of endogenous(同源的)stem cells.

    According to Zhang, endogenous stem cells are different from other stem cells that are typically grown in a laboratory, transplanted into a patient, and can have risks of immune（免疫的）rejection, infection or cancers. Zhang told CBS News, “We invented a new operation to make a very small opening at the side of a cataractous lens bag, remove the cataract inside, allow the opening to heal, and promote potential lens stem cells to regrow an entirely new lens with vision.”

    The human trial involved 12 babies under the age of 2 who were treated with the new method, while 25 babies received thee standard operation care.. The latter group experienced a higher incidence of pos- operation danger, early- onset eye high blood pressure and increased lens clouding. The scientists reported fewer complications and faster healing among the 12 babies who has the new procedure.

    Most people know precious gemstones (宝石) by their appearances. An emerald flashes deep green, a ruby seems to hold a red fire inside, and a diamond shines like a star. It's more difficult to tell where the gem was mined, since a diamond from Australia or Arkansas may appear the same to one from the Democratic Republic of the Congo. However, recently, a team of scientists has found a way to identify a gemstone's origin.

    Beneath the surface of a gemstone, on the tiny level of atoms and molecules（分子）, lie clues (线索) to its origin. At this year's meeting of the Geological Society of America in Minneapolis, Catherine McManus reported on a technique that uses lasers (激光) to clarify these clues and identify a stone's homeland. McManus directs scientific research at Materialytics, in Killeen, Texas. The company is developing the technique. “With enough data, we could identify which country, which mining place, even the individual mine a gemstone comes from,” McManus told Science News.

    Some gemstones, including many diamonds, come from war-torn countries. Sales of those “blood minerals” may encourage violent civil wars where innocent people are injured or killed. In an effort to reduce the trade in blood minerals, the U.S. government passed law in July 2010 that requires companies that sell gemstones to determine the origins of their stones.

    To figure out where gemstones come from, McManus and her team focus a powerful laser on a small sample of the gemstone. The technique is called laser-induced breakdown spectroscopy. Just as heat can turn ice into water or water into steam, energy from the laser changes the state of matter of the stone. The laser changes a miniscule part of the gemstone into plasma, a gas state of matter in which tiny particles（微粒）called electrons separate from atoms.

    The plasma, which is superhot, produces a light pattern. (The science of analyzing this kind of light pattern is called spectroscopy.) Different elements produce different patterns, but McManus and her team say that gemstones from the same area produce similar patterns. Materialytics has already collected patterns from thousands of gemstones, including more than 200 from diamonds. They can compare the light pattern from an unknown gemstone to patterns they do know and look for a match. The light pattern acts like a signature, telling the researchers the origin of the gemstone.

    In a small test, the laser technique correctly identified the origins of 95 out of every 100 diamonds. For gemstones like emeralds and rubies, the technique proved successful for 98 out of every 100 stones. The scientists need to collect and analyze more samples, including those from war-torn countries, before the tool is ready for commercial use.

    Scientists like Barbara Dutrow, a mineralogist from Louisiana State University in Baton Rouge, find the technique exciting. “This is a basic new tool that could provide a better fingerprint of a material from a particular locality,” she told Science News.

    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.

    Mexico sites on an island plateau (高原) surrounded by volcanic peaks, which makes air quality a constant concern for people who live there.

    In April, the country took a decisive step toward improving air quality by enacting a temporary ban on private and Federal vehicles in the city. The rule forbids people from driving in the city one day each week and one Saturday each month. Electric vehicles, government service vehicles, public transport options and school buses are not included in the ban.

    Mexico City isn't the first urban center to be involved in car-free living. But the ban is more than an awareness-raiser. It was enacted with the direct aim of solving air pollution. In March, the city sank into a deep brown haze of smog when the pollution levels passed the 200 mark. The city ordered some 1.1m of the area's 4.7m cars off the streets and also offered free bus and subway rides.

    Mexico City's temporary vehicle ban raises questions about the best ways to improve urban air quality. India, whose citizens breathe some of the world's dirtiest air, has tried a variety of solutions. Earlier this year, the Indian government started a 4% sales tax on new-car purchases.

    Beijing also has experience with cleaning the air. The city introduced alternate-day rules in advance of the 2008 Olympic Games, which produced good results. And then there is the London congestion (拥挤) charge, introduced in 2003. The charge has had a measurable effect on air quality.

For now, Mexico City — named by the United Nations as the most polluted city on the planet in 1992 — can look forward to the start of the region's rainy season, when daily showers will help lo clean the air.

    From American Express, wedding guests will, on average, spend $673 on each wedding they attend this year. It includes airfare （$225）, hotel （$170）, dining out （$116）and dressing up （$95）and the gift. If you have weddings to attend this year, here are some tips for you to avoid breaking the bank.

    ⒈Book flights in advance

    The moment you decide to attend a wedding is the time to check flight prices at the best time. Plane fares are higher in the summer, especially in July and August. Booking in advance will save you money, as will watch for sales on lower﹣cost carriers like JetBlue and Frontier. You can check Google Flights for a calendar of prices showing the cheapest days to fly from apps like Hopper to get real﹣time alerts when a fare is at its lowest price point.

    ⒉Don't blow your budget on the gift

    If you've got the money, an expensive gift is lovely. But there's no need to take out loans to prove your love for the happy couple. Skip an expensive necklace by giving （an appropriate amount of） cash instead. To save on the gift, consider making one： A photo album or scrapbook of memories with the bride and groom shows how much you care. You could also share the gift with other guest(s) or even make gifts with DIY ideas by yourself to save money.

    ⒊Use old dresses and suits

    You don't always have to be on a new dress for a wedding. While men have the option of repeating their suits, women are more likely to spend money on new clothes for the special occasion. But before you take out your wallet, consider reinventing something already in your closet. Belts, colorful scarves, shoes can bring life to any outfit.