You are presented with the quiz "Telephones are used for communication by two people by transmitting waves produced by what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "telephones are used for communication by two people by transmitting sound" and "all sounds are waves produced by the vibrations of material objects". 

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


 

     the vibrations of objects      