三个重物m1、m2、m3用一绕过两个定滑轮M和N的绳子相连，如图所示。当重物m1下降时，重物m2在四棱柱ABCD的上面向右移动，而重物m3则沿侧面AB上升。若三个重物的质量均为M；四棱柱的质量为9M，它置于水平光滑面上，开始物系静止。当重物m1下降h时，四棱柱的位移为（　　）。题48图

A、<img width="46" height="38" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/1adf3c4b-b705-44af-93c5-b2a30e432792.png" />

B、<img width="45" height="38" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/bcc8a534-f694-4478-a68b-cdddd588cdca.png" />

C、<img width="45" height="38" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/ac67d5bc-6bc1-4e4c-b1af-a089afdfef81.png" />

D、<img width="54" height="38" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/d17ba8a4-fca3-4171-8526-6f46bd66c866.png" />