The correct option is (a) Clarifiers
Explanation: Soil slurry reactors contain slurry which is usually thickened and dewatered using Clarifiers and presses, whereas Biosparging is the technique which is used to re-mediate contamination at the boundary level of water table, Immobilization uses Bio-accumulation processes, bio-degradation is the process that leads to degradation of compounds with the help of bacteria.