At which level does the regulation of gene expression occur?

Where are the regulatory genes located in an operon?

The functioning of structural genes is controlled by:

Consider the following statements of gene regulation and select the correct statements $:$
$(A)$ Expression of genes is regulated by metabolic,physiological,or environmental conditions.
$(B)$ Galactose can act as an inducer for the lac operon.
$(C)$ The operator region is adjacent to the promoter elements in most operons.
$(D)$ In the lac operon,lactose is transported into the cell through the action of permease.
$(E)$ Regulation of the lac operon by a repressor is referred to as positive regulation.

What does an operon represent?

$A$ low level of expression of lac operon occurs at all the time. Can you explain the logic behind this phenomenon?