A geostrophic wind is the result of pressure gradient force being balanced by coriolis force with no other forces involved so it is only found where we have straight parallel isobars.   This rules out answers (a) and (d).   It is a wind due to pressure differences at the surface, not temperature differences, so that rules out answer (b).   The goestrophic wind scale is not used to calculate wind speeds near the equator or the poles but it is used between 15º - 20º N/S and up to 80ºN/S so answer (c) is the correct one.