The two links OA and OB are connected by a pin joint at O. If the link OA turns with angular velocity ω1 rad/s in the clockwise direction and the link OB turns with angular velocity ω2 rad/s in the anti-clockwise direction, then the rubbing velocity at the pin joint O is

• A. ω1.ω2.r
• B. (ω1-ω2)r
• C. (ω1+ω2)r
• D. (ω1-ω2)2r