The correct option is D both b and c
The host cell which is genetically engineered to carry a gene of interest is known as a recombinant cell. The gene of interest is transcribed and translated to produce the recombinant protein.
The type of culturing method in which recombinant cells are grown in culture conditions maintained at a steady state is known as continuous culture. It is characterised by draining out used culture medium from one side of the bioreactor accompanied with simultaneous addition of fresh medium from the other side.
Such a culture method ensures that there is continuous supply of nutrients and the cells maintain exponential growth in the culture. Due to this, the cells in a continuous culture grow and result in a large biomass. As the number of cells in the culture media increases exponentially, the amount of desired protein expressed by them also increases. This helps to obtain higher yields of desired proteins.