Describe the streamlines of the given velocity field v(x, y, z) = - yi + xj.
◦ concentric circles centred on the x-axis in planes perpendicular to the x-axis
◦ concentric circles centred on the z-axis in planes perpendicular to the z-axis
◦ hyperbolas in planes perpendicular to the z-axis
◦ parabolas in planes perpendicular to the z-axis
◦ concentric circles centred on the y-axis in planes perpendicular to the y-axis