What role do cAMP and CAP play in transcription of lac operon genes?

A) CAP binds the CAP binding site of the lac promoter to carry out negative control of operon gene transcription, whereas cAMP blocks the CAP binding site and thereby allows fine-tuning of the system.

B) CAP and cAMP form a complex that binds the CAP binding site of the lac promoter to carry out negative control of operon gene transcription.

C) CAP binds the CAP binding site of the lac promoter to carry out positive control of operon gene transcription, whereas cAMP blocks the CAP binding site and thereby allows fine-tuning of the system.

D) CAP and cAMP form a complex that binds the CAP binding site of the lac promoter to carry out positive control of operon gene transcription.