A magnetic field $\overrightarrow{\mathrm{B}}=\mathrm{B}_{0} \hat{j}$ exists in the region $a \lt x \lt 2 a$ and $$\overrightarrow{\mathrm{B}}=-\mathrm{B}_{0} \hat{j}$$, in the region $2 a \lt x \lt 3 a$, where $\mathrm{B}_{0}$ is a positive constant. A positive point charge moving with a velocity $\vec{v}=v_{0} \hat{i}$, where $v_{0}$ is a positive constant, enters the magnetic field at $x=a$. The trajectory of the charge in this region can be like,