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智能手机上已普遍使用电阻接触屏.如图在竖直方向上触摸屏相当于一根电阻丝,触摸P 点时电阻丝被分为上、下两部分.电阻分别为R1、R2电源电压不变,当触摸点在竖直方向移动时,若测得R1两端电压减小,则R2阻值____,触摸点P 到屏下端的距离____(选填“增大”、“减小”或“不变”).

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增大,增大

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    What would the world be like if cars could drive themselves? Imagine seeing an empty car passing by on its way to pick up its owner, or a car full of passengers who are reading, listening to music or even sleeping, but none of them are worried about the road ahead.

Well, all of this could be the future of driving. There are several companies, including Google, working on driverless (无人驾驶的) cars, which are currently in the testing stages. If the tests are successful, these electric, self-driven cars could be available very soon. But, how is it possible for a car to drive itself?

    Cars already have many features allowing them to take over for drivers in certain situations. Some features include cars being able to park themselves, or slow down when they detect objects (物体) close by. They can also control the speed if there are dangerous conditions, such as snow or slippery (滑的) roads.

    Other features have also changed the way drivers react to some situations. Scientists and engineers believe, with the help of wireless signals, cameras and GPS, we are now at a stage where creatinga safe self-driving car might be possible.

    The self-driven car may be the answer to lowering the number of deadly (致命的) accidents caused by careless drivers or dangerous conditions. However, there are still some people who do not like the idea. American lawyer Whit Drake, for example, doesn't believe these cars are safe. He thinks the possibility of the technology making a mistake will be too high.