Answer:
B. the presence of cyclic AMP and lactose
Explanation:
Maximal transcription of the lac operon requires the presence of cyclic AMP and lactose. Cyclic AMP/CRP complex attached to a specific sequence in the lac control region. This region is known as the "CAP" site. Mutations that occurs in the CAP site prevent cyclic AMP-CRP binding which also prevent high levels of expression of the lac operon. The lac repressor and catabolite activator protein (CAP) are the two regulators that is responsible for turn on and off the operon in response to lactose and glucose levels.
