E Coli Cells Achieve a Great Deal of Gene Regulatory $\sigma$

Multiple Choice

E. coli cells achieve a great deal of gene regulatory expression through the $\sigma$ subunit of RNA polymerase. Which $\sigma$ subunit is present most often since it promotes the production of most of the proteins required under normal conditions within the cell?

A) $\sigma$ ^N
B) $\sigma$ ^S
C) $\sigma$ ^H
D) $\sigma$ ³⁰
E) $\sigma$ ⁷⁰