Here is an astonishing and significant fact：Mental work alone can't make us tire. It sounds absurd．But a few years ago, scientists tried to find out how long the human brain could labor without reaching a stage of fatigue(疲劳). To the amazement of these scientists, they discovered that blood passing through the brain, when it is active, shows no fatigue at all!

    If we took a drop of blood from a day laborer, we would find it full of fatigue toxins (霉素) and fatigue products. But if we took blood from the brain of an Albert Einstein, it would show no fatigue toxins at the end of the day.

    So far as the brain is concerned, it can work as well and swiftly at the end of eight or even twelve hours of effort as at the beginning. The brain is totally tireless. So what makes us tired?

    Some scientists declare that most of our fatigue comes from our mental and emotional (情绪的)attitudes. One of England's most outstanding scientists, J. A. Hadfield, says, “The greater part of the fatigue from which we suffer is of mental origin. In fact, fatigue of purely physical origin is rare. ”Dr. Brill, a famous American scientist, goes even further, He declares, “One hundred percent of the fatigue of sitting worker in good health is due to emotional problems.”

    What kinds of emotions make sitting workers tired? Joy? Satisfaction? No! A feeling of being bored, anger, anxiety, tenseness, worry, a feeling of not being appreciated— those are the emotions that tire sitting workers. Hard work by itself seldom causes fatigue. We get tired because our emotions produce nervousness in the body.

    While the U.S. is still debating about getting rid of the penny, Sweden is rapidly moving towards abolishing currency altogether. Though this may sound radical(过激的), it is a natural evolution in this digital society.

    Sweden, which was the first European country to introduce banknotes in 1661, has just been working harder to convince its residents that digital payments are a safer alternative to carrying cash.

    Over the years, the idea has gained popularity with residents, especially the younger generation that is much more comfortable with technology. Today many banks don't even have ATMs and some have stopped handling cash altogether!

    Tickets to ride public buses in most Swedish cities can only be purchased via cell phones. Numerous businesses are also moving towards accepting only digital payments. Even the homeless that sell street paper to make ends meet have to start accepting this mode of payment!

    But despite its growing popularity, some people don't like this radical idea. They include the homeless, elderly people as well as those living in rural areas who are still uncomfortable with mobile phones and computers. But the officials are confident that in the very near future, they will be able to convince everyone to move this safe and more cost-effective payment system.

    Sweden is not the only country trying to abolish paper currency and coins. The movement is rapidly gaining ground in Denmark and Finland as well. In 2014, Israel announced a three-step plan to go cashless and just last week the vendors(小贩)of a popular street in Sydney declared they would stop accepting currency from customers. Whether this phenomenon spreads remains to be seen. But one thing is for sure—With increasingly advanced payment systems being introduced every day, pulling out cash is rapidly becoming “uncool”.

    I climbed Kilimanjaro with Lava Expeditions (探险队) during the rainy season.

    I flew to Nairobi in Kenya and spent several days there. At my hotel in Nairobi I met the rest of the group with whom I would spend the next week. We all travelled on the bus together for a 6-hour journey into Tanzania and then Arusha, a quiet town.

    After we arrived at our hotel in Arusha, we had dinner and a few drinks. Then we were introduced to more members including Taddeus Minja, the main guide, who was very experienced — climbing Kilimanjaro runs through the generations (代) of his family.

    The next day the Lava Expeditions members checked if we had the correct and enough clothing for our expedition on Kilimanjaro. Only one person needed to bring more clothes.

    After that we set off, walking in the rain through the beauty of the rainforest, all the way to the first camp. I was happy the next few days as the view was so wonderful and changed every day. I suffered a little during the trip and I felt so tired. But the members of Lava Expeditions provided me with lots of encouragement, which was one of the best memories. Finally we reached the top of Kilimanjaro in bright blue skies.

I felt excited about climbing Kilimanjaro and the feeling didn't change during my trip. Lava Expeditions looked after me so well that I was deeply thankful for their help.

    Colorado officials will stick to a plan to kill some mountain lions and bears to support the state's dropping mule deer (长耳鹿) population.

    Wednesday's vote permits organizations to kill up to 25 black bears and 15 mountain lions per year in the central and western parts of the state. The project will run for three years, to be followed by a six-year study of how deer populations respond to fewer predators(捕食者).

    The population of Colorado's mule deer has suffered a puzzling, years-long drop to about 450,000, which state officials said was about 110,000 fewer than there should be. A 2014 state study tied it to seven causes, including predators, whose number has greatly increased in recent years.

    Some experts, however, said the state should focus first on the human-led destruction(破坏) of mule deer habitat(栖息地). “The drop of the mule deer population is obviously not a simple problem with simple causes,” Brian Kurzel, director of the National Wildlife Federation, said. “By far, the greatest problem—the one that I think deserves the most attention in any science-based study—is habitat quantity and quality.”

    Kurzel pointed out that the U.S Bureau of Land Management recently agreed to create 15,000 new oil and gas wells somewhere in western Cororado, which was often called “the mule-deer factory”. There, the number of mule deer has fallen to about 30,000 from more than 100,000 in the early 1980s. Though state officials have known oil and gas development affects the population of mule deer, they didn't go against the plan.

    Other causes like building highways, population growth and human activities are also curbing the mule deer population, according to the study.

    State Parks and Wildlife officials don't necessarily disagree. They started a $4.5 million program as a way to gather research for later decisions.

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    I always felt sorry for the people in wheelchairs. Some people, old and weak, cannot get around by themselves. Others seem perfectly healthy, dressed in business suits. But whenever I saw someone in a wheelchair, I only saw a disability，not a person.

    Then I fainted(昏倒) at Euro Disney due to low blood pressure. This was the first time I had ever fainted, and my parents said that I must rest for a while after first aid. I agreed to take it easy, but as I stepped toward the door, I saw my dad pushing a wheelchair in my direction! Feeling the colour burn my cheeks, I asked him to wheel that thing right back to where he found it.

    I could not believe this was happening to me. Wheelchairs were fine for other people but not for me. As my father wheeled me out into the main street, people immediately began to treat me differently.

    Little kids ran in front of me, forcing my father to stop the wheelchair suddenly. Bitterness set in as I was thrown back and forth.

    "Stupid kids! They have perfectly good legs. Why can't they watch where they are going？"I thought. People stared down at me，pity in their eyes. Then they would look away, maybe because they thought the sooner they forgot me the better. "I'm just like you!" I wanted to scream "The only difference is that you've got legs，and I have wheels."

    People in wheelchairs are not stupid. They see every look and hear each word. Looking out at the faces, I finally understood: I was once just like them. I treated people in wheelchairs exactly the way they did not want to be treated. I realized it is some of us with two healthy legs who are truly disabled.