A charged particle moves through a region of space at constant velocity. Ignore gravity. In the region,

Question:

A charged particle moves through a region of space at constant velocity. Ignore gravity. In the region, is it possible that there is
(a) A magnetic field but no electric field?
(b) An electric field but no magnetic field?
(c) A magnetic field and an electric field? For each possibility, what must be true about the direction(s) of the field(s)?