A particle of mass $m$ and charge $q$ is released from rest at the origin as shown in the figure. The speed of the particle when it has travelled a distance $d$ along the $z$ -axis is given by:
(a) $\sqrt{\left(\frac{2 q E_{0} d}{m}\right)}$
(b) $\sqrt{\left(\frac{E_{0} d}{B_{0}}\right)}$
(c) $\sqrt{\left(\frac{m}{q E_{0} d}\right)}$
(d) $\sqrt{\left(\frac{2 m}{q E_{0} d}\right)}$