You are presented with the quiz "What has electrical current running through it when working properly?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "when an electrical circuit is working properly , electrical current runs through that circuit" and "much of the circuit is in fact a comparator made with discrete transistors". 

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


 

      Discrete transistors.     