You are presented with the quiz "Blowing air into what causes air to move inside it?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "blowing air into a whistle causes air to vibrate inside the whistle" and "when an object moves or vibrates, the air molecules around the object also vibrate". 

So, what's the best answer to the question?


 

     whistle      