题干

如图所示,不同元素的二价离子经加速后竖直向下射入由正交的匀强电场和匀强磁场组成的粒子速度选择器,恰好都能沿直线穿过,然后垂直于磁感线进入速度选择器下方另一个匀强磁场,偏转半周后分别打在荧屏上的M、N两点.下列说法中不正确的有(   )

A:这两种二价离子一定都是负离子

B:速度选择器中的匀强磁场方向垂直于纸面向里

C:打在M、N两点的离子的质量之比为OM:ON

D:打在M、N两点的离子在下面的磁场中经历的时间相等

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D

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    Two of the saddest words in the English language are if only. I live my life with the goal of never having to say those words, because they convey regret, lost opportunities, mistakes, and disappointment.

    My father is famous in our family for saying, “Take the extra minute to do it right.” I always try to live by the “extra minute” rule. When my children were young and likely to cause accidents, I always thought about what I could do to avoid an “if only” moment, whether it was something minor like moving a cup full of hot coffee away from the edge of a counter, or something that required a little more work such as taping padding (衬垫) onto the sharp corners of a glass coffee table.

    I don't only avoid those “if only” moments when it comes to safety. It's equally important to avoid “if only” in our personal relationships. We all know people who lost a loved one and regretted that they had foregone an opportunity to say “I love you” or “I forgive you.” When my father announced he was going to the eye doctor across from my office on Good Friday, I told him that it was a holiday for my company and I wouldn't be here. But then I thought about the fact that he's 84 years old and I realized that I shouldn't give up an opportunity to see him. I called him and told him I had decided to go to work on my day off after all.

    I know there will still be occasions when I have to say if only about something, but my life is definitely better because of my policy of doing everything possible to avoid that eventuality. And even though it takes an extra minute to do something right, or it occasionally takes an hour or two in my busy schedule to make a personal connection, I know that I'm doing the right thing. I'm buying myself peace of mind and that's the best kind of insurance for my emotional well-being.