You are presented with the question "Cold air advancing on warm air cause what?" and the following answer choices: 
- Greenhouse gases
 - friction
 - flooding
 - wind storms
 - colder weather
 - air storms
 - ice storms
 - thunderstorms

Now knowing that cold fronts cause thunderstorms as they pass by and if cold air is advancing on warm air, the front is called a cold front, choose the best answer.


 

        thunderstorms 