Usually, a mutation in the promoter region of an operon causes reduced levels of synthesis of the proteins encoded by that operon. Occasionally, a mutation in the promoter region actually causes increased levels of synthesis. Can you suggest (briefly) a plausible explanation?

Explanation:

The possible explanation of the increased synthesis of the protein by an occasional mutation in the promoter is that the mutation could occur in the enhancer sequence

This specific region, enhancer are 200 base pair long DNA elements that is present either upstream or downstream to the transcriptional start site

Activity of enhancer is orientation independent and provide binding site for activators(activators are large proteinaceous complex that initiate transcription)

d i think its   answer d