Could question 45 be wrong? Two solutions, one is heating only. Although the solubility of potassium nitrate has increased, no solute has been added, so the solute mass fraction of solute solvent solution has not changed, but the solubility has changed. The other only adds solute, and the temperature remains unchanged. Because it is a saturated solution, the solubility does not change, and potassium nitrate will not absorb water when dissolved in water, so the added solute does not dissolve, so the quality of solvent and solute does not change, and the quality of solution naturally does not change. The concentration of solution is the mass of solute divided by the mass of solution, and then multiplied by 100%. But the solute mass and solution mass of the two solutions have not changed just now, so the concentration has not changed. Just now, the solubility in the first solution has changed, so the ABD has not changed, only C has changed.

For question 46, if you choose a, the quality of the solution should be increasing and will not remain the same.