Correct Option: C

Lac operon is an inducible operon. Lactose is the substrate for the enzyme betagalactosidase and it also regulates switching on and off of the operon. Hence, it is termed as inducer. Inducers function by disabling repressors. The gene is expressed because an inducer binds to the repressor. The binding of the inducer to the repressor prevents the repressor from binding to the operator. RNA polymerase can then begin to transcribe operon genes.