Q: Fact 1: Cold fronts cause thunderstorms as they pass by. Fact 2: If cold air is advancing on warm air, the front is called a cold front. Given the two facts above, where do thunderstorms come from?

Possible answers: 1. Too much rain in the clouds; 2. When the environment is too cold; 3. Earth's axis of rotation is tilted; 4. fissures of hot, acidic water; 5. More than one trophic level.; 6. it flows to a lower level; 7. Dryness in the environment; 8. When cold air advances on warm air;
A:
8.