Apparently, the thicker spring has higher k, and the thinner spring has lower k. the spring with the lower k can be affected ( extended ) by small amount of force such as wind which gives an error in determining the mass. in that case, it should be kept in a rigid box to insulate it from any other external forces ( wind ). whereas in the thicker spring, the external forces are negligible because it needs much more force to be extended ( since it has a high k value). So A is the answer.arlery said:Why is the answer A?