The correct option is C Bioreactor
Bioreactors are required for growing microbes on a large scale for the industrial production of enzymes. These large vessels with appropriate conditions of pH, temperature, nutrients, aeration, etc. provide a biologically active environment. These controlled conditions promote reactions at optimum pace and provide yields at large scale.
On the other hand, sludge digesters are used to decompose organic solid waste. BOD incubators are used to maintain the appropriate temperature for test tissue culture growth, storage of bacterial cultures, etc. Industrial ovens are used for a variety of processes like drying, curing, etc.