What is the difference between a repressible and an inducible operon?

The primary difference between repressible and inducible systems is the result that occurs when the effector molecule binds to the repressor. ... Thus, for the trp operon , the addition of tryptophan (the effector molecule) to the E. coli environment shuts off the system because the repressors binds at the operator.

Explanation:

the answer for this question would be d. glaciers

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.