Here is an astonishing and significant fact: Mental work alone can't make us tire. It sounds absurd. But a 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(毒素) 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.

    Below is a selection from a popular science book.

    If blood is red, why are veins（静脉）blue?

    Actually, veins are not blue at all. They are more of a clear, yellowish colour. Although blood looks red when it's outside the body, when it's sitting in a vein near the surface of the skin, it's more of a dark reddish purple colour. At the right depth, these blood-filled veins reflect less and light than the surrounding skin, making them look blue by comparison.

    Which works harder, your heart or your brain?

    That kind of depends on whether you are busy thinking or busy exercising. Your heart works up to three times harder during exercise, and shifts enough blood over a lifetime to fill a supertanker. But, in the long run, your brain probably tips it, because even when you're sitting still your brain is using twice as much energy as your heart, and it takes four to five times as much blood to feed it.

    Do old people shrink as they age?

    Yes and no. Many people do get shorter as they age. But, when they do, it isn't because they're shrinking all over. They simply lose height as their spine（脊柱）becomes shorter and more curved due to disuse and the effects of gravity（重力）. Many (but not all) men and women do lose height as they get older. Men lose an average of 3-4 cm in height as they age, while women may lose 5 cm or more. If you live to be 200 years old, would you keep shrinking till you were, like 60 cm tall, like a little boy again? No, because old people don't really shrink! It is not that they are growing backwards – their legs, arms and backbones getting shorter. When they do get shorter, it's because the spine has shortened a little. Or, more often, become more bait and curved.

    Why does spinning make you dizzy（眩晕的）?

    Because your brain gets confused between what you're seeing and what you're feeling. The brain senses that you're spinning using special gravity-and-motion-sensing organs in your inner ear, which work together with your eyes to keep your vision and balance stable. But when you suddenly stop spinning the system goes out of control, and your brain thinks you're moving while you're not!

    Where do feelings and emotions come from?

    Mostly from an ancient part of the brain called the limbic system. All mammals have this brain area – from mice to dogs, cats, and humans. So all mammals feel basic emotions like fear, pain and pleasure. But since human feelings also involve other. Newer bits of the brain, we feel more complex emotions than any other animal on the planet.

    If exercise wears you out, how can it be good for you?

    Because our bodies adapt to everything we do to them. And as far as your body is concerned, it's use it, or lose it”! It's not that exercise makes you healthy; it's more that a lack of exercise leaves your body weak and easily affected by disease.

    Below are some best special interesting holidays─all are new for 2017 and have high quality guides or tutors and strong programmes.

    Holland in bloom river cruise (巡游) with Alan Titchmarsh

    Alan Titchmarsh is the star attraction on this river cruise. Alan joins you for a visit to the magnificent Keukenhof Gardens─home to 800 varieties of tulips (郁金香).The Telegraph's gardening expert will talk about the best new varieties and the garden's history.

    April 19, £1,495 including flights from the UK and some meals. Telegraph Tours (0161 236 2444; telegraph.co.uk/titchmarshtour).

    Morocco Sketchbook

    Led by artist Maxine Relton, this tour takes in Marrakesh helping you develop your drawing skills. Rapid line and figure drawing and colour mixing are all covered and the eight-day holiday is based in Kasbah du Toubkal.

    May 8, £2,495 including some meals. Steppes Travel (01285 601 495; steppestravel.co.uk).

Ballroom and Latin American dancing in Tenerife

    This travel provides daily dance tuition with David Bowie who'll be on hand to teach dancing techniques. It is aimed both at the beginners and more experienced dancers looking to improve their skills. There'll also be time to explore the island on foot or play a round of golf.

    April 26, £769 full-board. Saga (0800 096 0084; travel.saga.co.uk).

    Fishing in Northern Argentina

    This nine-day fly fishing and conservation tour takes in the Iberá Marshlands, the world's second largest wetlands. Here expert fisherman, Charles Jardine, is the guide as you fish. Based in Estancia Rincon del Socorro, the holiday also includes opportunities for horse riding and bird-watching.

    October 15, £5,095 full-board. Cazenove + Loyd (02038135082; cazloyd.com).

    There's a new frontier in 3D printing that's beginning to come into focus: food. Recent development has made possible machines that print, cook, and serve foods on a mass scale. And the industry isn't stopping there.

    Food production

With a 3D printer, a cook can print complicated chocolate sculptures and beautiful pieces for decoration on a wedding cake. Not everybody can do that—it takes years of experience, but a printer makes it easy. A restaurant in Spain uses a Foodini to" re-create forms and pieces" of food that are" exactly the same,” freeing cooks to complete other tasks. In another restaurant, all of the dishes and desserts it serves are 3D-printed, rather than farm to table.

    Sustainability(可持续性)

    The global population is expected to grow to 9.6 billion by 2050, and some analysts estimate that food production will need to be raised by 50 percent to maintain current levels. Sustainability is becoming a necessity. 3D food printing could probably contribute to the solution. Some experts believe printers could use hydrocolloids( 水解胶体)from plentiful renewables like algae(藻类) and grass to replace the familiar ingredients(烹饪原 料). 3D printing can reduce fuel use and emissions. Grocery stores of the future might stock "food" that lasts years on end, freeing up shelf space and reducing transportation and storage requirements.

    Nutrition

    Future 3D food printers could make processed food healthier. Hod Lipson, a professor at Columbia University, said, "Food printing could allow consumers to print food with customized nutritional content, like vitamins. So instead of eating a piece of yesterday's bread from the supermarket, you'd eat something baked just for you on demand."

    Challenges

    Despite recent advancements in 3D food printing，the industry has many challenges to overcome. Currently, most ingredients must be changed to a paste( 糊状物)before a printer can use them, and the printing process is quite time-consuming, because ingredients interact with each other in very complex ways. On top of that, most of the 3D food printers now are restricted to dry ingredients, because meat and milk products may easily go bad. Some experts are doubtful about food printers, believing they are better suited for fast food restaurants than homes and high-end restaurants.

    They say the average person makes 35, 000 decisions a day. Yet in her new book, How Woman Decide, Therese Huston explores a widespread phenomenon that many women fail to notice. "There's a huge double standard when it comes to how men and women are viewed as decision﹣makers," explains Therese, a psychologist from Seattle University. Therese decided to write the book after looking at her bookshelf: At one end, there were bestselling books about how to be a clever decision﹣maker ﹣ all written by men and featuring interviews with men like athletes. At the other end were books aimed at women on gaining leadership skills and confidence.

    "Once those women are at the table, will their decisions be taken as seriously as men's？" Therese wondered. "Men are respected as decision﹣makers more than women, especially in the workplace, largely because there's this cultural belief that women are unable to make smart choices at work. "

    So, Therese set out to pick apart the stereotypes（固有印象）to see what scientific research had found. "Scientific research shows that men and women struggle with decision-making equally. The only disadvantage I found was that during the teenage years-teenage girls are more indecisive than teenage boys. Otherwise, there's little difference between the genders（性别）.

    However, there are some differences. "Women are more collaborative（协作的）, "says Therese. "A female boss is more likely to ask the opinions of those around her when making a choice. Women ask for input, which helps make better decisions. However, this is often seen as a weakness rather than a strength.

    Therese also found that during times of stress, men and women make different choices, and the outcomes are often better when women are involved.

    Study after study backs this view up. Neuroscientists Mara Mather and Nicole Lighthall from the University of Southern California studied the way men and women make decisions and found that in times of stress, they react very differently.

    During their study, which involved playing a virtual gambling（赌博）game, they found that when the females became stressed, they made smart decisions ﹣ quitting while they were ahead or taking safe bets. But when the men became stressed, they did the opposite, risking everything for a slim chance of a big win.

    Dance Classes

    Ballet

    Ballet teaches grace, posture(姿势) and flexibility. Students focus on the use of proper ballet items(物品),expanding their knowledge of classical ballet techniques and improving motor skills for classical ballet practice. The class is a formal ballet class.

    Age 8-10

    September 7, 2019-May 16, 2020

    10:30 am-12:00 am on Saturday

    Creative Movers

    Students can explore creative movement, balance, focus, the development of skills, motor planning and balance. The class helps build strength, flexibility and self-confidence, and allows children to realize expression in a positive and encouraging environment.  Children use their imagination to celebrate movement and have lots of fun.

    Age 3-5

    September 7, 2019-January 18, 2020

    9:00 am-9:45 am on Saturday

    Jazz

    Jazz includes movements from both classical ballet and dance techniques. This class will focus on traditional jazz dance. Students will be introduced to jazz-style rhythms and movements. In order to ensure proper placement for your child, we invite all students to participate in a sample(示例) class. Students and parents work with program staff to meet students' personal dance goals.

    Age 5-6

    September 7, 2019-May 16, 2020

    2:00 pm-3:00 pm on Saturday

    Hip Hop

    Students will be introduced to several different aspects of hip hop dance including popping, locking, breaking and totting in a high-energy environment. Our hip hop instructors are highly knowledgeable and will provide students with a wonderful view of hip hop dance.

    Age 7-10

    September 7, 2019-May 16, 2020

    1:00 pm-2:00 pm on Sunday