How Is Sequential Gene Expression Controlled in Bacterial Viruses Like

Multiple Choice

How is sequential gene expression controlled in bacterial viruses like E.coli phages T7 and T4 and Bacillus subtilis phage SP01?

A) Modifying the DNA topology
B) Sequential binding of a series of repressor molecules
C) Modifying the specificity of RNA polymerase for different promoter sequences
D) Sequential binding of inducer molecules to the repressor
E) None of these are correct.