Which of the following BEST describes catabolite repression of the lac operon?
O Glucose is the preferred energy source for E. coli.
O The operon is transcriptionally inactive in the absence of lactose.
O The operon is transcriptionally active when an activator protein binds to the promoter in the absence of glucose.
O The operon is transcriptionally inactivated by a repressor protein, which binds to glucose.
O The operon is repressed by its protein products.