You are presented with the question "what converts wind energy into electricity" and the following answer choices: 
- clouds
 - mechanical waves
 - windpower operated machines
 - Movement of an air mass
 - solar panels
 - Warm air moving into cold air
 - batteries
 - tectonic plates being pushed together

Now knowing that awindmill converts wind energy into electricity primarily by using mechanical energy and windmills are machines operated by windpower, choose the best answer.


 

   windpower operated machines      