Concept: Well water often contains dissolved calcium or magnesium hydrogencarbonates, making it hard and unsuitable for lathering soap.
Explanation:Hard water prevents soap from forming a good lather, which is needed for laundry.
Boiling removes temporary hardness by precipitating the dissolved salts.
Filtering only removes suspended particles, not hardness.
Adding chlorine disinfects water, but does not soften it for laundry.
Therefore, boiling is the simplest method shown.
Answer: C. boiling