Achieving "Zero Pollutant Discharge" in Water,as Stipulated by Some Laws

Achieving "zero pollutant discharge" in water,as stipulated by some laws is in practice difficult because

A) Many analytical instruments are incapable of detecting substances present at very low, but nonzero, concentrations.
B) No water-treatment process is completely efficient at removing pollutants.
C) Treatment costs escalate exponentially as pure water is approached.
D) All of the choices are correct.