The surface mass density of a disc of radius a varies with radial distance as o = A+ Br where A&B are positive constants the moment of inertia of the disc about an axis passing through its centre and perpendicular to the plane (A) 2mat ( + D) 4 (B) 2mat (4 + ) (B) 2ra (+ ) (C) ra Ba (D) 2ma* ( Ba