At what level does gene expression not occur?

Define an operon,give an example,and explain an inducible operon.

In $lac$ operon,the regulator gene codes for

Select two correct statements from the four $(a-d)$ given below regarding the $lac$ operon.
$(A)$ Glucose or galactose may bind with the repressor gene and induce inactivity.
$(B)$ In the absence of lactose,the repressor binds with the operator region.
$(C)$ The $z$-gene codes for permease.
$(D)$ This was elucidated by Francois Jacob and Jacques Monod.
Which of the following are the correct statements?

Which of the following is true for a repressible operon?

Which of the following binds to the repressor,causing the repressor and the operator to dissociate from each other?