You would want to identify the part that sets the sound in motion. For example, the cello(my instrument), produces it's sound from the forced vibration of one or more of its four strings. But if you are an alien looking at an old Yamaha keyboard that was on, you'd press a key to find that the sound came from the speakers. But in depth, you and the key were the producers, as you put energy into pressing the key to activate a circuit board, which in turn activates the speakers. So I would say the answer is A.
