Two observers moving with different velocities see that a point charge produces same magnetic field at a point $A$. Their relative velocity must be parallel to , $\overrightarrow r$ where $\overrightarrow r$ is the position vector of point $A$ w.r.t. the point charge. This statement is

Question

$\begin {array} {1 1} (a)\;True \\ (b)\;False \\ (c)\;Nothing\: can\: be\: said \\ (d)\;True\: only\: if\: the\: charge\: is\: moving\: perpendicular \: to \: \overrightarrow r \end {array}$