The correct option is B Breakdown lactose
An operon is basically a regulatory system for genes in which a group of genes coding for like-functioning proteins are arranged linearly, and are under the control of a single regulator gene. When lactose is available to E.coli in its medium, the lac operon in the bacterial cell gets ‘switched on’, and works to break it down into glucose and galactose. In the absence of lactose, the operon would be in a ‘switched off’ mode, as there is nothing to be worked on.