Answer: Option D.
A region of DNA consisting of the promoter and operator sequences needed to regulate one or more structural genes.
Step-by-step explanation:
An operon is a part of the the DNA that is found in bacteria or viruses which function in transcription and genetic regulation. Operon is under control of an operator, consist of promoter, regulator and structural genes. Operon is normally under the control of a single operator in which genes coding for protein are clustered along the DNA.