4. The top layer of the steamer is cooked first. There is water under the steamed stuff. The water is boiled by heating. A large amount of water vapor above 100 degrees will go up, and then a lot of water vapor will gather on it. The water vapor is always the same because the heat source is always heating! Because the energy of water vapor is very high, it will move up sharply, so it stays underneath for a short time, and it is not easy to dissipate on it (the cover is to prevent the vapor heat from dissipating), which will increase the pressure of the uppermost layer and cause the uppermost thing. Easy to cook!