Which portion of sewage from primary treatment is taken for secondary treatment?

The correct option is B Effluent
Sewage treatment is carried in two steps: primary and secondary treatments.
Primary treatment steps basically involve physical removal of large and small particles from the sewage through filtration and sedimentation. All solids that settle in primary treatment form the primary sludge while the supernatant forms the effluent.
The effluent from the primary settling tank is taken for secondary treatment.