The appropriate answer is c. evaporation. Evaporation is the process by which a liquid changes to a gas and in this case is the best way to remove the water from the homogenous mixture. The reaction can be sped up by heating the mixture. All the water will eventually evaporate leaving behind the sodium chloride crystals as a precipitate.
Filtration works best on mixtures that have precipitates and distillation is for separating liquids with different boiling points.
