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 "Which situation can cause a thunderstorm?" with the following options: 
- Fog rising over a lake
 - pressure differences.
 - Earth's axis of rotation is tilted
 - Setting up lightning rods
 - Cold air advancing on cold air
 - Cold air advancing on warm air
 - Changing the angle of the sun
 - fall moving to winter


 

      Cold air advancing on warm air   