In the lactose operon of Escherichia coli, what is the function of promoter

Define an operon, giving an example, explain an Inducible operon.

In the medium where $E$. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?

An environmental agent that triggers transcription from an operon is a:

$A$ : Lac operon exerts negative control only.
$R$ : The operator is occupied by aporepressor during regulation