Right choice is (c) wood stain
The best I can explain: Vehicle is the preferred term, as the contents of a stain may not be truly ‘dissolved’ in the vehicle, but rather ‘suspended’, and thus the vehicle may not be a true ‘solvent’. The vehicle often may be water, alcohol, a petroleum distillate, or a finishing agent such as shellac, lacquer, varnish and polyurethane. Coloured or ‘stained’ finishes do not typically deeply penetrate the pores of the wood and may largely disappear when the finish deteriorates or is removed.