A small particle of mass \(m\) and positive charge \(q\) moves along the \(x\)-axis in a region where the electric potential is given by \(V(x) = C x^4\), where \(C > 0\) is a constant and \(V(0) = 0\). The particle is released from rest at position \(x = x_0\). Assuming no non-conservative forces act on the particle, which of the following graphs best represents the particle's velocity \(v\) as a function of position \(x\) during one full oscillation between \(x = -x_0\) and \(x = x_0\)?