题干

如图所示,将水平金属导轨、可沿导轨移动的垂直导轨的金属棒放在磁场中,和电流表组成闭合电路,下列几种操作,电流表中有电流的是(   )

A:导体棒在磁场中不动时

B:导体棒做切割磁感线运动时

C:导体棒连同金属导轨平行于磁感线运动时

D:以上操作都没有电流产生

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B

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    Fei-Fei Li arrived in the U. S. from China at age 16 with many big dreams. And it took many unusual jobs to help her achieve them. Luckily, she was smart and extremely driven. And today, she's the director of Stanford University's artificial intelligence lab.

    As one of the leaders in the world for A. L., I feel much excitement and responsibility to create the most awesome and excellent technology for society and to educate the most awesome and excellent technologists—that's my calling.” Li said.

    She is also a loyal advocate for diversity in the tech industry.

    “I see extremely talented Stanford PhD students struggling with their visas and I find it unthinkable that we create so many barriers for the talents of the world, Li said. While Li was in college at Princeton, she borrowed money from friends and even her high school math teacher to run a dry-cleaning business for her parents in order to help them get by. Li attended classes during the week and worked at the business on the weekends. Then, when Li was in graduate school, her mom developed cancer and had a stroke (中风). It was difficult to keep moving ahead while all of this was happening. The real existential challenge is to live up to your fullest potential, live up to your sense of responsibility and to be honest to yourself about your dreams while doing it, she said.

    Li was named a Great Immigrant of 2016 by the Carnegie Corporation, the nation's oldest grant making foundation which honors roughly 40 naturalized U. S. citizens each year. Her graduate studies were supported by the Paul & Daisy Soros Fellowships for New Americans.