Electric pendulum

As shown above, a charged particle is hanging on the top of two parallel plates. A voltage of $V$ generates a uniform electric field inside the plates. If we lift up the charged particle to the point $x$ and then let it go, the charged particle oscillates between $x$ and $z$ with $y$ the center point of the oscillation. Which of the following statements is correct? (Ignore gravity, air resistance and the generation of electromagnetic waves.)

a) The electric potential at the point $x$ is greater than that at the point $y.$

b) The period of the oscillation decreases as the voltage $V$ increases.

c) The magnitude of the electric force acting on the charged particle at the point $x$ is greater than that at the point $y.$