已知杆AB和CD自重不计，且在C处光滑接触，若作用在AB杆上力偶的矩为，则欲使系统保持平衡，作用在CD杆上力偶的矩的转向如图所示，其矩值为（　　）。题49图

A、<img width="61" height="24" src="http://admintk.100xuexi.com/UpLoadImage/2016-10-26/bf23cbab-724a-4cc4-8d97-88cf569ad7be.png" />

B、<img width="88" height="24" src="http://admintk.100xuexi.com/UpLoadImage/2016-10-26/ca7b8f68-ef5d-4ab1-8c92-d1239e114383.png" />

C、<img width="69" height="24" src="http://admintk.100xuexi.com/UpLoadImage/2016-10-26/4c46d730-ce9b-4c3c-b6b7-7c7d5a479360.png" />

D、<img width="68" height="24" src="http://admintk.100xuexi.com/UpLoadImage/2016-10-26/01d2556c-cd04-4140-b2ff-56fdbb820bc3.png" />