A particle of mass m and with charge q moves with a speed v describing a path in the form of circumference of radius r, due to the presence of a magnetic field perpendicular to the trajectory of modulus or magnitude B. Recalling that the modulus of the centripetal acceleration is a = v/r , the radius r, is given by: a) qB/mv b) mq/vB c) mv/qB d) vB/mq