The charged particles of an infinitely long and filamentary wire produce a linear charge density ' and

The charged particles of an infinitely long and filamentary wire produce a linear charge density λ' and a current I'. Let the vector I' = I' ẑ indicate the direction of current flow.
(a) What is the current I and linear charge density λ measured in the laboratory frame when the wire moves with velocity v = νẑ in that frame?
(b) Show that, by an appropriate choice of inertial frame, one can reduce the magnetic field of the wire to zero or one can reduce the electric field of the wire to zero. In the first case, find the linear charge density responsible for the remaining electric field. In the second case, find the current responsible for the remaining magnetic field. Why is only one of these choices possible?