钱穆在《国史新论》中论述古代某一制度时说“自经此制度推行日久，平民社会，穷苦子弟，栖身僧寺，十年寒窗，也可跃登上第”。有关这一制度的说法正确的是（   ）

    Hello! I'm Ben. This is my new living room. It's quite big. There is a chair and two big sofas. There are some flowers beside the sofa. Between the sofas, there is a lovely cat. There aren't any pictures but a clock o n the wall. There is a computer on the desk next to the sofa. There is a TV set on the TV stand(电视柜) under the window. I often watch TV in my living room. What a nice living room.

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在人体体细胞增殖的一个细胞周期中，在纺锤体形成时，一个细胞中的染色体数为N，DNA含量为m；则当该细胞中染色单体消失时，此细胞中的染色体数和DNA含量分别是