Task: Question Answering
Input (English): Question: A coulometric evaluation: 
 Options:  <1> You do not need the current performance to be 100%. <2> It does not need an indicator system of the end point. <3> Always use a potentiostatic system. <4> It uses a titrant that is generated electrolytically. <5> You need a burette to add the titrant.
Output (English): 4