If when a comparator made with discrete transistors is working properly , electrical current runs through it, then what has electrical current running through it when working properly?

Answer choices:
- a hydraulic system
 - Marathon runners.
 - deoxyribonucleic acid
 - The bending of a ray of light
 - Electrical tape.
 - Discrete transistors.
 - Ocean currents.
 - electromagnetic energy

 

      Discrete transistors.    