① The intersection of two curves in the solubility curve indicates that the solubility of the two substances is equal at this temperature, so it can be seen from the image that the solubility of substance A and substance B is equal at 20℃;

(2) The solubility changes of A and B are different from 40℃ to 20℃, and the change of A is more obvious. Therefore, when saturated solutions of equal mass of A and B are cooled to 20℃ respectively, the most crystals are precipitated.

③ At 40℃, the solubility of substance B is 40g. According to the definition of solubility, the maximum mass of substance B that can be dissolved in 100g water at 40℃ is 40g, so the mass of water required to completely dissolve 60g of substance B at 40℃ to obtain a saturated solution is 60g×100g =150g;

④ The point on the solubility curve indicates that the solution is saturated at this time; Point B under the curve indicates that the solution at this temperature is unsaturated; The solution shown at point A above the curve is a saturated solution containing undissolved solute.

So the answer is: ① 20;

②A；

③ 150;

④B。