The rotor of 3-phase slip ring induction motor is fed from a 3-phase supply with its stator winding short circuited having rotor rotating clockwise at a speed of Nr, then the

• A. speed of air gap field w.r.t. stator is ns-nr anticlockwise
• B. speed of air gap field w.r.t. stator is ns-nr clockwise
• C. speed of airgap field w.r.t rotor is ns clockwise
• D. speed of airgap field w.r.t. stator is ns-nr clockwise