Answer:
The correct answer would be operon.
Operon can be defined as a functional unit of the DNA which consists of structural gene and regulatory element such as promoter, operator, and repressor.
It may contain many structural genes under the control of single promoter. All the genes are transcribed as single mRNA which undergoes different types of splicing to produce different functional proteins.
For example, lac operon contains three functional genes lac Z, lac Y, and lac A together with promoter and operator sites.