题干

小红用托盘天平测量一枚大头针的质量.

(1)不能将一枚大头针放到托盘天平上进行直接测量,原因是____ ;

(2)增减砝码后发现指针略偏于分度盘中央刻度线的左侧,接着的正确操作是 ____ 

A.将横梁右端的平衡螺母向右移动        

B.将横梁有端的平衡螺母向左移动

C.减少天平右盘中的砝码      

D.向右移动标尺上的游码

(3)测量多枚大头针质量,所加砝码及游码位置如图所示,若已知一枚大头针的质量约为80mg,此时测量所加的大头针数量约为 ____  枚.

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答案(点此获取答案解析)

一枚大头针质量太小,D,900

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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.