(9) [10 points] A charged particle with charge q and mass m is initially at the origin with a initial velocity $v=v_{0}\hat{z}$ along the z-axis. The particle is in a nonuniform magnetic field: $B(x,y)=-y\hat{x}+x\hat{y}$. What is the work done by the magnetic field along the trajectory when the particle moves a distance L along the z direction?(A) $mv_{0}^{2}/2$(B) $mv_{0}^{2}/L$(C) 0(D) $mv_{0}^{2}/q$(E) $v_{0}^{2}L/q$