Fact 1: Cold fronts cause thunderstorms as they pass by.

Fact 2: Thunderstorms Thunderstorms give birth to tornadoes.

Given the two facts above, answer the question "What causes tornadoes? " with the following options: 
- Electrical energy
 - scattered light
 - hypothyroidism
 - Time and energy
 - harmful substances
 - Cold fronts.
 - Tropical
 - heat energy


 

      Cold fronts.   