Explanation

(b) Let E and B be along X-axis. When a charged particle is released from rest, it will experience an electric force along the direction of electric field or opposite to the direction of electric field depending on the nature of charge. Due to this force, it acquires some velocity along X-axis. Due to this motion of charge, magnetic force can not have non-zero value because angle between v and B would be either $0^{0}$ or $180^{0}.$ So, only electric force is acting on particle and hence, it will move along a straight line.