杆OA绕固定轴O转动，长为l。某瞬时杆端A点的加速度a如图4-2-1所示。则该瞬时OA的角速度及角加速度为（　　）。[2014年真题]图4-2-1

A、<img width="50" height="32" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/fa83dab8-2ce8-4d4a-9e8f-1fbc2ac48be4.png" />

B、<img width="108" height="40" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/8fa8a8ba-358e-472b-94fb-87b35f649434.png" />

C、<img width="58" height="38" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/440c1c9d-bf76-4bdf-980d-bdb3cfcfbb85.png" />

D、<img width="63" height="40" src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/ef4f2e5e-9ed9-4c35-a73c-b36dfaed1623.png" />