Just to confuse the issue but to add information, I expect a probably is the correct answer because it is true. However, some water is hard and it isn't from Ca and Mg salts but Fe or Mn salts. The Fe and Mn salts discolor clothes; therefore, I consider b true also. Then c is true, too, although some soft water may cause them. Finally, the DIRECT RESULT part of the statement troubles me a little. The bath tub ring is caused by the action of SOAP with the Ca and Mg salts in hard water to form the scum. Therefore, without the soap, the bath tub ring would not appear so easily nor so prominently. The DIRECT RESULT isn't so direct if we consider that soap AND hard water are necessary to cause the ring. In addition, some soaps aren't made from animal fat and they don't cause the severe bath tub sum we see with ordinary soap when using hard water. Personally, I think the person making the question/answers should edit this one.
