Which of the following best describes the biological role of the lac operon?

A. It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.
B. It prevents other sugars from being metabolized until all available lactose has been used.
C. It ensures that a cell produces enzymes involved in lactose metabolism in a constitutive manner.
D. It ensures that bacterial cells produce lactose only when no other food sources are available.