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 "Cold air advancing on warm air cause what?" with the following options: 
- Greenhouse gases
 - friction
 - flooding
 - wind storms
 - colder weather
 - air storms
 - ice storms
 - thunderstorms


 

        thunderstorms 