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    Every year, hundreds of millions of Monarch Butterflies(黑脉金斑蝶) from Canada and the United States journey as far as 2, 500 miles to the forests of Michoacan, Mexico, a place which has the world's largest insect migration(迁移). It's such a breathtaking sight, but as always, human greed is threatening to destroy it.

    The Monarch Butterflies start to arrive in Michoacan in late October to make their winter home in the trees high up in the mountains of the natural reserve. Once there, they gather together in large masses. These masses often become so heavy that they cause tree branches to bend or even break. But there's a purpose of all these massing — it allows the butterflies to survive in the low nighttime temperatures at these high altitudes.

    The Michoacan Monarch Butterfly Sanctuary is most impressive during the months of February and March, just before the winged insects begin their long journey home.

    Mexico's Butterfly Forest is a shelter protected by law, and one of the country's most popular sights, but that hasn't stopped people from slowly but steadily destroying it.

    Illegal woodcutting in the heart of the Monarch Butterfly Biosphere Reserve has been a longstanding problem, but criminals are rarely brought to justice. They are often set free after paying some money.

    Just last month, an even greater threat rose in Michoacan's butterfly home.  The country's largest mining corporation gained the right to reopen an old mine in the heart of the monarch reserve. Experts believe that if the mine is reopened, it will likely spell the end of this magical place.

    And as if all this wasn't bad enough, the increasing use of herbicides（除草剂） in the American corn belt has led to the decrease of  a plant which is essential to the monarchs' development from egg into butterfly.

    Nobody likes doing the dishes, but it turns out that doing this daily task might pay off in an unexpected way. According to a new study published in the Journal of Pediatrics, washing dishes by hand instead of using a dishwasher might prevent the development of allergies.

    Researchers in Sweden surveyed the parents of 1,029 children ages 7 and 8. They discovered that children whose families hand-washed the dishes instead of using a machine were less likely to have allergies.

    Earlier research has shown that dishes washed by machine are cleaner than those washed by hand. So why would kids who eat off slightly dirtier plates be better off when we talk about preventing allergies? One explanation is based on a theory known as the "hygiene hypothesis (卫生假说)," which says the reason why kids develop allergies is that their surroundings are actually too clean.

    Your immune (免疫) system keeps you healthy by fighting germs (病菌) like bacteria and viruses. But when you have allergies, it overreacts and tries to fight ordinary things like pollen (花粉) or certain foods.

    Being exposed to germs, particularly early in life, is good training for the immune system, says the lead author of the study, Dr. Bill Hesselmar of Queen Silvia Hospital in Sweden. "You excite the immune system in various ways and it becomes tolerant."

    This study shows that while using the dishwasher might be easier, the old-fashioned method of cleaning up could be better for your health.

    A cellphone is one of the few things that we hold close to our faces all the time, and yet it could possibly explode - this is what made the recent Samsung's Galaxy Note 7 smart-phone accidents so shocking.

   According to technology news website The Verge, flawed（有瑕疵的）phone batteries might be to blame.

    Even if you are not a science student, you probably know that it is common sense that the anode (the negative（负的）end of the battery) and the cathode (the positive end) should never touch. If they do, the battery will short-circuit（短路）, causing a powerful electrical reaction that can destroy the battery and cause a fire.

    This is why all lithium-ion（锂离子）batteries - the kind that can be found in many of our devices like tablets and cameras - have a separator layer inside to stop the two ends from touching one another.

    But somehow, the separators in some of the Samsung phones broke, causing explosions.

    Overcharging is another problem that can make batteries heat up quickly. Fortunately, most batteries are designed to be able to automatically stop charging once they are fully charged. But again, this somehow failed to happen in some of the Samsung phones.

    The two “somehows” may sound random（随机的）and hard to explain. But they actually both come from the fact that phone producers have been pushing the limits of batteries to meet customers' demand for a longer battery life.

    According to Lynden Archer, a materials scientist at Cornell University, US, we have already achieved 90 percent of the battery life possible from a lithium-ion battery. Customers' demand that their devices get thinner has also given producers little choice but to try to put more power into thinner batteries.

     “The more energy you put into a box, the more dangerous it's going to be,” Billy Wu, a lecturer at Imperial College London, told The Guardian.

    A thinner battery also means producers have to use thinner material for separators, and thinner material has more chance of breaking.

    Not long ago, a good friend of mine asked me to help him in a halfway house in Nashville. I agreed and made my way there one evening.

    When I got there, I sat with my friend and talked about how he ended up there. As we talked, another man came up, lighting up his cigarette as he sat down. He had dark, leather skin, and looked like he had endured the sun, the rain, and the wind for long, long time. I couldn't tell how old he was, but I was sure that he was younger than he looked.

    Through a bit of conversation, I found out that he had been on the streets for many, many years.

    Without my asking, he started describing life as a homeless man. How he got food; how he stayed warm; how he got money. And he told me something that caught my attention.

    He said, "You want to know how I keep my stuff safe at night?"

    "Sure," I replied.

    "I put it up in the trees."

    "Why is it safe in the trees?" I asked.

"The homeless are always looking for treasure on the ground— coins, something someone's dropped, half-smoked cigarettes. I know if I put my stuff in the trees, they'll never find it because they never look up. Never. "

    Profound words from an unexpected place. And his message is for all of us.

We all have our particular search. We're looking for treasure on this earth. But what we are REALLY looking for is right there above us. There's really nothing we need on the ground.

    In fact, it's surrounding us.

    Chinese media and Internet users on Monday decried（谴责）a lack of morals in society after a child was struck twice by two different trucks and left bleeding on the road as more than a dozen bystanders did nothing to help the seriously injured girl.

    The incident, captured by a surveillance camera and aired by Southern Television Guangdong (TVS), showed the two-year-old girl was knocked down and run over by a white truck on a narrow market street on the afternoon of Oct. 13, in Foshan City of Guangdong Province.

    The driver fled the scene of the accident, leaving the girl to bleed on the sidewalk. Over the next six minutes, more than a dozen people walked by the girl, yet not one individual did anything to help her. The girl was then hit a second time by another van before an elderly trash collector came to her aid and brought the attention of the girl's mother, according to the video and eyewitnesses.

    Doctors said that the girl, who was put on life support after being hospitalized, remains in a deep coma. The girl's parents, who are migrants living in the city, are now with her.

    Police said the drivers of both vehicles have been arrested. However, the apathy(冷漠) of the bystanders shown in the video has shocked the public, and people are questioning the morality of society.

    High moral standards were once considered as national pride in China where individuals known for selflessly helping others were adored（崇拜） by the public.

    But in recent years, the perception（观念）of a decline of morals has become a hot topic as profit and materialism are perceived to be affecting society's values.

    On Sept. 2. an 88-year-old man in central China collapsed, his face striking the pavement. Yet, no one came to his aid, and he ended up choking to death on the blood from his nose.

    Some have linked the absence of good Samaritans (模范人物)to a previous case in which a man trying to help an elderly woman who fell was accused of harming her.

    A strong chorus of opinion on the Internet says laws should exempt（免除）Samaritans from liability（责任）, yet laws themselves cannot solve society's morality dilemma.

    Cao Lin, a China Youth Daily commentator, said in a signed article published on Monday that the worry of liability should not be an excuse for not helping, and this case exposes the decline of humanity in Chinese society.

On an autumn afternoon, a remote sheep farm in southern Greenland is quiet. The silence is abruptly broken when dozens of sheep come thundering across the hills overlooking the farm. Walking after them are Lars Nielsen and his 37-year-old son Kunuk Nielsen.

The Nielsen family has owned and run the farm since 1972. Kunuk says the summers now are longer than when he was a child and that drought has become a problem. The fields are not so green as those in the old days. He has to buy hay (草料) from European countries.

The effects of a warming climate are obvious on the land. While he intends to struggle on, his older brother Pilu has chosen a different path.

Pilu, 40, lives in Qaqortoq in the south of Greenland -- a town of about 3,000 people. Ten years ago, he got his helicopter pilot's license and is now part owner of a small company called Sermeq Helicopters. It caters to construction and telecommunication workers and an increasing number of foreign tourists.

Pilu says he loves his family's sheep farm. But he saw that warming temperatures were making remote areas of Greenland more accessible and wanted to look for other opportunities. His company's most popular tours include a visit to Greenland's glaciers.

The warming temperatures are also affecting traditional ways of life, particularly hunting. The sea ice is changing; it's becoming less so that hunting on ice becomes more difficult. When there's no sea ice, it's difficult to use dog sledges (雪橇), and the whole culture around having dogs and dog sledges and doing traditional hunting on the ice is sort of diminishing.

Besides, many Greenlanders, like Pilu, are leaving the countryside for towns and the capital city Nuuk, where opportunities are greater. A report found that Nuuk's share of Greenland's population grew from 17.2% in 1977 to 29.2% in 2014. If there were enough houses in Nuuk, the share would even be bigger.