Which one of the following represents the correct sequence of different component genes in a $lac$-operon?

• A
  Regulator $\rightarrow$ Promoter $\rightarrow$ Operator $\rightarrow$ $lac \ Z \rightarrow lac \ Y \rightarrow lac \ A$
• B
  Operator $\rightarrow$ Promoter $\rightarrow$ Regulator $\rightarrow$ $lac \ A \rightarrow lac \ Y \rightarrow lac \ Z$
• C
  Promoter $\rightarrow$ Regulator $\rightarrow$ Operator $\rightarrow$ $lac \ Z \rightarrow lac \ Y \rightarrow lac \ A$
• D
  Regulator $\rightarrow$ Promoter $\rightarrow$ Operator $\rightarrow$ $lac \ A \rightarrow lac \ Y \rightarrow lac \ Z$