As self — driving cars come closer to being common on American roads, much of the rhetoric (说辞) promoting them has to do with safety. About 40,000 people die on U. S. roads every year, and driver errors are linked to more than 90 percent of crashes. But many of the biggest advocates of autonomous vehicles aren't car companies looking to improve the safety of their existing products. Huge backing for self - driving technologies is coming from Silicon Valley giants like Google and Apple.

    Those of us who have studied the relationship between technology and society tend to look more carefully at the motivations behind any technological push. In this case, it's clear that in addition to addressing safety concerns, Silicon Valley firms have a strong incentive (动机) to create a new venue for increasing the use of their digital devices. Every minute people spend on their mobile phones provides data - and often money - to tech companies.

    At present, digital devices and driving are in conflict: There are serious, often fatal, consequences when drivers use smartphones to talk or to text. Regulators and safety advocates look to resolve dial conflict by banning phone use while driving - as has happened in virtually every state. But the tech companies are taking a different approach. The obvious answer for Silicon Valley is creating an antomobile in which continuous cellphone use no longer poses a threat to anyone.

    In recent years, the amount of time adults spend on their mobile devices has grown rapidly. At the moment, it's around four hours a day for the average adult in the U. S. However, that rapid growth is likely to slow down as people run out of time that ' s available for them to use their devices. Unless, of course, there's a new block of time that suddenly opens up. The average American now spends about 48 minutes in a car every day, a sizable opportunity for increased cellphone use.

    So as the public conversation around autonomous cars highlights the safety advantages, don't forget the tech industry ' s powerful desire for more profits, which goes well beyond simply saving us from ourselves.

    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.

    The National Postal Museum is divided into galleries that explore America's postal history. Visitors will have a full picture of the creation and fantastic varieties of postage stamps.

    World of Stamps

    Video images bring stamps to life and attract visitors who explore the surrounding displays. Visitors encounter the world's first postage stamp — the 1840 Penny Black and learn how it revolutionized communication. Stamp images, including Dr. Martin Luther King's "I have a dream" speech and the stamp that helped raise almost $72 million dollars for breast cancer research, explain how stamps have shaped history and honored people and places worldwide.

Gems of American Philately

    Visitors have the opportunity of examining 13 of the most rare and highly valued stamps in the world of the stamp collection, including the most famous American stamp of all, the 1918 Inverted Jenny. A video explains why the Inverted Jenny and other stamps displayed here are the most valuable. The treasures in this area are rarely available for public viewing. Each tells a story about an important event in US history.

    Mail Marks History

    The markings on mail provide valuable clues to the surprising ways mail has been transported over time, including challenges and even disasters encountered along the way. You will understand these markings by following the journeys of three historic letters.

    Connect with US Stamps

    Visitors explore their own connections with stamps. At three touch screen tables, they create their own stamp collection based on the topics that interest them most. They can also create their own stamp designs. Visitors have the chance to view videos in which stamp designers talk about their craft, stamp collectors explain what they collect and why, and footage(片段) shows the process of making stamps.

    Canada is a very large country. It is the second largest country in the world. By contrast it has a very small population. There are only about 29 million people there. Most Canadians are of British or French origin, and French is an official language of Canada as well as English. About 45% of the people are of British origin, that is, they or their parents or grandparents, etc., come from Britain. Nearly 30% are of French origin. Most of the French-Canadians live in the province of Quebec.

    Over the years, people have come to live in Canada from many countries in the world. They are from most European countries and also from China, besides other Asian countries.

    However, Canada was not an empty country when the Europeans began to arrive. Canadian Indians lived along the coast, by the rivers and lakes and in forests. Today there are only about 350, 000 Indians in the whole country, with their own languages. In the far north live the Inuit. There are only 27, 000 Canadian-Inuit. Their life is hard in such a difficult climate.

    Next month, I'm traveling to a remote area of Central Africa and my aim is to know enough Lingala — one of the local languages — to have a conversation. I wasn't sure how I was going to manage this — until I discovered a way to learn all the vocabulary I'm going to need. Thanks to Memrise, the app I'm using, it feels just like a game.

    "People often stop learning things because they feel they're not making progress or because it all feels like too much hard work," says Ed Cooke, one of the people who created Memrise. "We're trying to create a form of learning experience that is fun and is something you'd want to do instead of watching TV."

    Memrise gives you a few new words to learn and these are "seeds" which you plant in your "greenhouse". When you practice the words, you "water your plants". When the app believes that you have really remembered a word, it moves the word to your "garden". And if you forget to log on (登录), the app sends you emails that remind you to "water your plants".

    The app uses two principles about learning. The first is that people remember things better when they link them to a picture in their mind. Memrise translates words into your own language, but it also encourages you to use "mems". For example, I memorized "motele", the Lingala word for "engine", using a mem I created — I imagined an old engine in a motel (汽车旅馆) room.

    The second principle is that we need to stop after studying words and then repeat them again later, leaving time between study sessions. Memrise helps you with this, because it's the kind of app you only use for five or ten minutes a day.

    I've learnt hundreds of Lingala words with Memrise. I know this won't make me a fluent speaker, but I hope I'll be able to do more than just smile when I meet people in Congo. Now, I need to go and water my Vocabulary!

It was the middle of winter some 30 years ago. I was a young father with three little mouths to 1 . My college education, however, didn't help me to 2 a well-paid job. I was working in a woodcutting business for just above the 3 wage. Working outdoors for 8 hours a day had caused my4 to split (裂开) and bleed at their tips in the cold, dry air. 

That day at work was harder than normal. We 5 workers. Worse still, the machines kept breaking down. When the day finally ended, I took off the gloves and 6 my painful hands. The splits were 7 than ever and I had bled through the band-aids again. I tried to 8 my back but it hurt badly. I had never felt that tired and 9 before, wondering why life was so tough and how long I could keep doing this. 

I tried to 10 a smile as I got home. My daughter ran up to me merrily, yelled "Daddy!", and 11 her little arms around my neck. My heart exploded with 12 . My aches and tiredness disappeared into her13 . And the joy in my heart 14 the depression away. At that moment I knew I could continue on and that things would get better. 

We all have 15 fingers and band-aid days in our lives here. But with love we can make it through them all.