This involves "metal activity", and the common metal activities are "potassium, calcium, sodium, magnesium, aluminum, zinc, iron, tin and lead (hydrogen)". The metal in front can replace the metal in the back (in short, the elders are in front and the younger generation will give up their seats when they come), while yogurt generally contains acid (that is, hydrogen), so if you use an iron spoon, iron will replace hydrogen. .