Coli Colonies Grown on a Lactose-Containing Medium Up-Regulate the Production

coli colonies grown on a lactose-containing medium up-regulate the production of the enzymes Beta-galactosidase and galactoside permease.  Which of the following best explains the synchronous production of both enzymes in response to lactose?

A) There are two activator binding sites for one activator protein
B) There are two operators for one repressor protein
C) There are two repressors for one inducer
D) There are two promoters in close proximity to each other
E) There is one mRNA coding for both enzymes