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在 2015 年北京田径世锦赛中,牙买加选手博尔特是公认的世界飞人,在“鸟巢”400m 环形赛道上,博尔特在男子 100m 决赛和男子 200m 决赛中分别以 9.79s 和 19.55s 的成绩破两项世界纪录,获得两枚金牌.关于他在这两次决赛中的运动情况,下列说法正确的是(   )

A:200 m 决赛中的位移是 100 m 决赛的两倍

B:200 m 决赛中的平均速度约为 10.23 m/s

C:100 m 决赛中的平均速度约为 10.21 m/s

D:100 m 决赛中的最大速度约为 20.42 m/s

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C

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Don't talk to me; I'm busy with my iPhone

    Riding a London subway, a person from China will notice one major difference: in London, people do not look at each other. In fact, eye contact is avoided at all times. That's not rudeness—people are just too busy to bother looking.

    Busy doing what, you ask? Well, they're certainly not using the time for a moment of quiet reflection, nor are they reading a book. New technology has replaced quiet habits. Today the only acceptable form of book on the London underground is an e-book.

    Apple company must earn a fortune from London commuters. Since the iPhone was put on market in 2007, over 40,000 --- yes, that's 40,000 “apps” (programs downloaded for the iPhone) have been designed.

    Commuters love them because they are the perfect time-fillers. One “app”, called iShoot, is a game that features tanks. Another one, Tube Exits, tells passengers where to sit on the train to be closest to the exit of their destination. ISteam clouds the iPhone screen when you breathe into the microphone. You can then write in the “steam” on your phone screen.

    For those without an iPhone, another Apple product, the iPod, may be another choice. It's not just teenagers who “plug in” to their music --- iPods are a popular way to pass the time for all ages.

    And if games, e-books and music aren't enough to keep you occupied. Then perhaps you would prefer a film. The development of palm DVD technology means many commuters watch their favorite TV show or film on the way to work. With all this entertainments, it's amazing that people still remember to get off the train.

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