Which simple method can obtain salt from salt water?

Correct answer: Evaporation

The governing concept is separation of a dissolved solid from a solution by using a difference in volatility. In salt water, sodium chloride is dissolved in liquid water, so the salt particles are too small to be retained by ordinary filter paper. On heating or leaving the solution in suitable conditions, water changes into vapour and escapes, whereas salt remains as a solid residue. This process is evaporation, so option A is correct. Magnetic separation requires a magnetic component, hand picking requires visible solid pieces, and filtration is useful for an insoluble solid, not for salt that has already dissolved.