有一质量为0.2kg的物块，从长为4m，倾角为30°光滑斜面顶端处由静止开始沿斜面滑下，斜面底端和水平面的接触处为很短的圆弧形，如图所示．物块和水平面间的滑动摩擦因数为0.2，求：（g取10m/s²）

《盛世危言》指出：“……置之，灾民流离困苦情形宛然心目。作奸犯科者，明正典刑，……中历历详述，见之者胆落气沮，不敢恣意横行，自有……，（士君子）足不逾户庭而周知天下之事……。”郑观应在此盛赞的是

    A man lived in a village. ____. The cat couldn't run fast, and she couldn't bite, because she was so old. One day, when she saw a mouse, she jumped and caught it. ____. The mouse got out of her mouth and ran away.

    ____ and began to beat the cat. The cat said, “____. I know I'm old and can't kill a mouse. But I have worked for you for many years, and I still want to work for you. ____, and remember what good work they did when they were young.”

    When the man heard that, he realized that he was wrong.