Which of these is a regulatory gene?
A. structure of the lac operon. It contains definite structures labeled from A to E. Letter A marks a gen before structural genes.
B. marks a part of the operon that consists of lac Z, lac Y, and lac A genes.
C. indicates a structure that moves along the operon.
D. marks lac l. This part is located before the others in the sequence.
E. indicates a molecule that can bind to structure A.