The role of silver iodide in artificial rainfall is meteorologically called cold cloud catalysis. When heated, silver iodide forms extremely fine (only one to one-thousandth of the hair diameter) silver iodide when heated. Particles.1g of silver iodide can form tens of trillions of microparticles. These particles will enter the cloud with the movement of airflow, generating tens of trillions to trillions of ice crystals in cold clouds. Therefore, the use of silver iodide to catalyze rainfall does not require airplanes, equipment It is simple, with very little usage and low cost, and can be promoted on a large scale. Based on this text, we can speculate that the reason why silver iodide catalyzes rainfall without the need for an airplane is (). ['Silver iodide particles move into the cloud with the airflow.', 'Silver iodide will form silver iodide particles as long as it is heated.', 'Cold cloud catalysis enables silver iodide to form tens of trillions of particles.', 'Particles can generate trillions to trillions of ice crystals in cold clouds.']