题干

物体在水平桌面上,在水平拉力作用下沿着力的方向做匀速直线运动,则(  )

A:桌面对物体的滑动摩擦力与水平拉力是一对作用力和反作用力

B:桌面对物体的滑动摩擦力与物体对桌面的滑动摩擦力是一对作用力和反作用

C:物体对桌面的压力与桌面对物体的支持力是一对平衡力

D:物体所受的重力与物体受到的支持力是一对作用力和反作用力

上一题 下一题 0.0难度 选择题 更新时间:2019-12-24 11:11:41

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B

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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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