Answer:
B. binds to the tryptophan repressor when the repressor is bound to tryptophan.
Explanation:
Bacterial genes are commonly composed of operons that are activated or deactivated depends on the needed. If the bacteria need, for example, an amino acid such as tryptophan for synthesizing proteins. An activator "turns on" the transcription that the operon has and produces the amino acid.
On the other hand, if the bacteria have a high presence of tryptophan amino acid, a repressor binds to the tryptophan operator and avoids the amino acid transcription, in consequence, constrain the tryptophan production.
