Did you know that sixty percent of your body weight is water? However, a loss of only two percent of this water through dehydration (脱水) during exercise can significantly affect your performance. The more you sweat, the more your exercise performance declines, unless you drink enough to replace your loss of fluids (液体).

    When you lose too much water, you can overheat quite easily, especially in a warm environment. But this is not the only problem you may face. Dehydration leads to your heart pumping much faster, which means exercise becomes more difficult and requires more effort. Despite these problems, however, many of us simply do not take enough fluids in when we head for the gym or set out on a run.

    So why is this? How do we manage to lose so much water without simply drinking more to replace it? Well, it's easier than you think. When we are at rest, we quickly become aware that we are thirsty and will put that right by having a drink. When we exercise, on the other hand, our thirst mechanism (结构) does not work as effectively, so we don't notice early enough that we are actually thirsty. In fact, we only start to fed thirsty when we have already lost around two percent of our body weight.

    Another problem is that, the more dehydration we become during exercise, the more difficult it is to prevent further dehydration-because our stomachs become intolerant (不能容忍的) to fluids and we do not absorb water properly, just when we need it most.

    The key thing about fluids and exercise is to manage your intake properly-regular small amounts are preferable, and some should be drunk before the period of exercise begins. You also need to match your intake to the sort of exercise you are doing. For example, for one hour of exercise, such as taking part in a 10 km run, you need to drink about two extra litres of water. For longer periods of exercise, sports drinks are recommended.

    For most city people, the elevator is an unremarkable machine that inspires none of the enthusiasm or interest that Americans afford trains, jets，and even bicycles. Dr. Christopher Wilk is a member of a small group of elevator experts who consider this a misunderstanding. Without the elevator, they point out, there could be no downtown skyscrapers or tall buildings, and city life as we know it would be impossible. In that sense, they argue，the elevator's role in American history has been no less significant than that of cars. In fact, according to Wilk_? the car and the elevator have been locked in a “secret war” for over a century, with cars making it possible for people to spread horizontally (水平地)，and elevators pushing them toward life in close groups of towering vertical (垂直的)columns.

    If we tend to ignore the significance of elevators, it might be because riding in them tends to be such a brief, boring, and even awkward experience^one that can involve unexpectedly meeting people with whom we have nothing in common, and an unpleasant awareness of the fact that we're hanging from a cable in a long passage.

    In a new book, Lifted, German journalist and cultural studies professor Andreas Bernard directed all his attention to this experience, studying the origins of elevator and its relationship to humankind and finding that riding in an elevator has never been a totally comfortable experience. “After 150 years, we are still not used to it”， Bernard said. “We still have not exactly learned to cope with the mixture of closeness and displeasure.” That mixture, according to Bernard, sets the elevator ride apart from just about every other situation we find ourselves in as we go about our lives.

    Today，as the world's urban population explodes，and cities become more crowded, taller, and more crowded, America's total number of elevators—900,000 at last count, according to Elevator World magazine's “2012 Vertical Transportation Industry”一are a force that's becoming more important than ever. And for the people who really, really love them, it seems like high time that we looked seriously at just what kind of force they are.

    Bike Share Toronto is the city's official bike share program, designed to give locals and visitors a fun, affordable and convenient alternative to walking, taxis, buses and the subway. There are 200 Bike Share Toronto stations and 2,000 bikes across the city, making Bike Share the most accessible way to get around and explore.

    How it works

    Become an Annual Member or buy a day Pass to access the system.

    Find an available bike nearby, and get a ride code or use your member key to unlock it.

    Take as many short rides as you want while your pass or membership is active.

    Return your bike to any station, and wait for the green light on the dock(停靠点)to make sure it's locked.

    Choose a plan

    For visitors

    Day Pass: $7. Unlimited 30-minute rides in a 24-hour period.

    3-Day Pass: $15. Unlimited 30-minute rides in a 72-hour period.

    For locals

    Monthly Pass: $25. Unlimited 30-minute rides for a month.

    Annual Membership: $90. Unlimited 30-minute rides for a whole year. The Annual Membership is the best deal for locals of Toronto and other frequent riders.

    The first 30 minutes of each ride is included with the membership or pass price. Avoid extra fees by dropping off your bike every 30 minutes at any other station. If you keep a bike out for longer than 30 minutes at a time, you will be charged an extra $1.50 for the first 30 minutes over, $4 for the next 30 minutes, and $7 for each additional 30 minutes after that.

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    Last summer, bird-watchers confirmed the discovery of a new species of bird in Cambodia was not an event of particular biological significance, but it was striking for one reason in part. This species of bird was discovered not in an unspoiled rain forest but within the limits Cambodia's capital, Phnom Penh – a city the size of Philadelphia.

What the researchers found was surprising in cities. The medium-sized city in the state about 110 species of birds, over 95 percent of which would have been growing there urbanization. Ecologically speaking, cities are different, concrete buildings. Rather, each unique bio-profile – a kind of ecological fingerprint – that is against the idea of an environment dead zone.

    Of course, it's also true that in the world of birds and plants, as in human society, there is such a thing as worldwide—the city-inhabitants who feel equally at home in San Francisco, Milan and Beijing. Four birds occur in more than 80 percent of the cities studied, and 11 plants occurred in more than 90 percent of the cities. On the plant side, those are seemingly spread by European settlement. In the air, it's the usual suspects: the rock pigeon and many other birds. “They have become completely adapted to urban life,”Katti says. “That's not much of surprise. But they don't actually dominate as much as we think they do.” Those species—occurring in the cities across the globe—represent only a small part of a city's natural varieties.

    Not all cities are equal protectors of native animals and plants, though. One of the biggest predictors for a city's biodiversity is its urban design. Territory as varied as backyards and street trees can lay important roles in greening a city. In fact, the amount of green space is a stronger predictor of the density of biodiversity than a city's size. A metropolis with a sizable network of parks can contain more species per square mile than a much smaller city.

    In a world where architecture, food, language, fashion and commerce are increasingly globalized, a city's native animals and plants can be a kind of identity. There may be neighborhoods in London and Paris that resemble Singapore or Hong Kong. Cities are becoming similar, but their natural environments stand completely apart.

    In 1978, I was 18 and was working as a nurse in a small town about 270 km away from Sydney, Australia. I was looking forward to having five days off from duty. Unfortunately, the only one train a day back to my home in Sydney had already left. So I thought I'd hitch a ride (搭便车).

    I waited by the side of the highway for three hours but no one stopped for me. Finally, a man walked over and introduced himself as Gordon. He said that although he couldn't give me a lift, I should come back to his house for lunch. He noticed me standing for hours in the November heat and thought I must be hungry. I was doubtful as a young girl but he assured (使…放心)me I was safe, and he also offered to help me find a lift home afterwards. When we arrived at his house, he made us sandwiches. After lunch, he helped me find a lift home.

    Twenty-five years later, in 2003, while I was driving to a nearby town one day, I saw an elderly man standing in the glaring heat, trying to hitch a ride. I thought it was another chance to repay someone for the favour I'd been given decades earlier. I pulled over and picked him up. I made him comfortable on the back seat and offered him some water.

    After a few moments of small talk, the man said to me, "You haven't changed a bit, even your red hair is still the same." I couldn't remember where I'd met him. He then told me he was the man who had given me lunch and helped me find a lift all those years ago. It was Gordon.

    Can you imagine a world without music？Studies show that public schools across the country are cutting back on music classes to save money. Worse, some schools have never had music classes to begin with. But without them, students' academic growth and emotional health could suffer. In fact, music classes are necessary for all students in schools.

    Recent studies by Brown University have shown that students who received music education classes were better in math and reading skills than those without music classes. Another study by The College Board found that students taking music and art classes got higher points. Students' academic success seems to depend on their taking part in music education.

    Music programs in public schools also help to add to a student's sense of pride and self-confidence. Teens today have too many learning tasks. Besides, they have family problems, self-confidence problems, relationship troubles, and choices about drugs and alcohol. All of these can stop academic success, but music education can help. A study by The Texas Commission on Drug and Alcohol Abuse found that students who took part in school music programs were less likely to turn to drugs. Music programs encourage students to work together to produce an excellent performance.

    Music crosses language, class, cultural and political boundaries (界限). Music allows students from different countries to connect. For example, at a school talent show, a new Japanese student played a piano duet (二重奏) with an American classmate. Although they could not communicate verbally (口头上), they were able to read the music in order to play the duet. Two students from different cultures worked as a team with self-confidence and common purpose through music.

    The gift of music is priceless. We need to be sure to have necessary music classes for all students. The world is losing its music, and putting music into schools is the first step to get it back.