The correct answer is C) Aeration, sedimentation, disinfection. In a biological sewage treatment plant with three chambers, the sequential order of treatment is as follows: 1. Aeration: This is the first stage, where air is introduced into the wastewater to promote the growth of aerobic bacteria that break down organic matter. 2. Sedimentation: The wastewater then enters a sedimentation chamber, where the treated effluent is allowed to settle, and the solid waste is removed. 3. Disinfection: The clarified effluent is then subjected to disinfection, typically through the addition of chlorine or other disinfecting agents, to kill any remaining pathogens before the treated water is discharged. The other options are incorrect because they do not represent the proper sequential order of the treatment chambers in a biological sewage treatment plant with three chambers.