In chemistry class, Mr  Zhang demonstrated two simultaneous teaching experiments: one is that O2 is produced slowly after KCIO3 heating; the other is that KCIO3 is heated and a small amount of MnO2 is quickly sprinkled into it, and a large amount of O2 is produced immediately
Teacher Zhang pointed out that MnO2 is the reason for the rapid production of O2
When Madame Curie extracted radioactive elements from bituminous minerals, she found that the radiation intensity of all pure uranium extracted from a certain amount of bituminous minerals was several times lower than that of the same amount of bituminous minerals. From this, she inferred that there are other more radioactive elements in asphalt minerals.