which of the following is true with respect to the lac operon?

a. the repressor only binds tothe operator when it is bound to the product of the enzymes coded for by the genes of the operon.
b. the repressor only bind to the operator when it is bound to the mRNA transcript of the lacZ and lacY genes.
c. the repressor only leaves the operator when it is bound to the  protein product of the lacI gene.
d. the repressor is always bound to the operator, but changes shape when lactose bind to it allowing RNA polymerase to pass.
e. the repressor is bound to the operator, except when it is bound to the inducer.