<prompt> In E.coli structural gene of lac operon is stimulated inPresence of glucose onlyPresence of lactose onlyPresence of glucose and absence of lactosePresence of lactose and absence of glucose  <response>: JACOB and MONAD theory was based on the observation on lactose metabolism in E.coli Cell grown in glucose medium does not contain beta-galactosidase But when cells are transferred to medium containing only lactose, then the enzyme level in the cell increases several thousand foldsRef: DM Vasudevan, 7th edition, page no: 617 