And so there's no need to form the tryptophan because the cell already has a high amount of tryptophan inside. But if the tryptophan concentration is low as the case is in part A, then what happens is we need to form more tryptophan so that the cell can function properly and effectively, so that the cell can form the many different proteins and enzymes that require this tryptophan amino acid. And so what will happen is our operon will be turned on because this inactive repressive protein will remain in its inactive form. It will not bind to the tryptophan because we will not have enough tryptophan inside that cell. So this is what we mean by a repressible operon. So a repressible operon is the most common type of opera that is used by bacterial cells when it comes to anabolic processes, processes in which we have to synthesize some type of important molecule.