If the velocity of a charged particle and magnetic field are at a fixed angle that is not 90 degrees, then the path will be:

Explanation

Force is given by F = qvBsinθ, where F, q, v and B are the force, charge on particle, velocity of particle and magnetic field strength respectively. θ is the angle between v and B.If θ = 0 or 180, there is no force on the particle and it continues to move with uniform velocity.If θ = 90, the force acting on the particle is maximum and perpendicular to the path of the particle. (force acts as a centripetal force and the particle moves along a circular path)When θ has a value other than 0, 90 or 180, the direction of velocity is either perpendicular or parallel to B. If the component of velocity is parallel to B it will not be affected by the magnetic field. However if the component of velocity is perpendicular to B it will be subject to a force of the magnetic field which would result in uniform circular motion. Hence the particle would have a component along a straight line as well as a circular component. Therefore the path would be in the form of a helix. And so option D is correct.