Stirred-tank bioreactors have been designed for: Availability of oxygen throughout the process, Ensuring anaerobic conditions in the cultural vessel, Purification of product, Addition of preservatives to the product

Stirred-tank bioreactors use an air compressor. The compressor generates air pressure to force the air through the filter, holes and into the liquid and thereby ensuring the continuous supply of oxygen throughout the process. Therefore, the correct answer is option A.