A charged particle is released from rest in a region of uniform electric and magnetic fields which are parallel to each other. The particle will move on a

When the particle is released from rest, it starts to move along the fields due to application of electric field. 
The magnetic force acting on a moving charged particle is given by 

$\vec{F}=q(\vec{v}\times \vec{B})$

Since velocity and magnetic fields are parallel, no magnetic force acts on the particle, hence it continues to move in a straight line along with constant acceleration.