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, answer the question "Where do thunderstorms come from?" with the following options: 
- Too much rain in the clouds
 - When the environment is too cold
 - Earth's axis of rotation is tilted
 - fissures of hot, acidic water
 - More than one trophic level.
 - it flows to a lower level
 - Dryness in the environment
 - When cold air advances on warm air


 

        When cold air advances on warm air 