An Alternating Current Is Supplied to a Lightbulb,which Strobes

An alternating current is supplied to a lightbulb,which strobes.A motor rotates a white fan (with one blade painted red) at 504 Hz in the light from the strobing bulb,and the fan appears to stand still.At 252 Hz the red blade alternates between two positions that are 180° apart.What is the angular frequency of the current? (Be careful,the light will strobe regardless of the sign of the current. )

A) 504π rad/s
B) 252π rad/s
C) 1008π rad/s
D) 126π rad/s