Corrosion needs the metal surface and the surrounding electrolyte to stay in direct contact so that metal ions can leave the surface and charge can flow between anodic and cathodic sites. A passive film, such as the thin chromium oxide layer on stainless steel or the aluminium oxide layer on aluminium, sits right on top of the metal and behaves like an insulating skin with very poor ionic conductivity. Because ions from the electrolyte can barely get through this skin to reach the bare metal underneath, the anodic dissolution reaction and the paired cathodic reaction are both starved of access to fresh metal surface, so the corrosion current drops sharply even though the metal underneath is still just as reactive as before. It is this loss of direct metal-electrolyte contact, not any change in current flow or dissolution pattern, that explains why passivation works. So the correct choice is option (C).