"Housekeeping Genes" in Bacteria Are Commonly Expressed Constitutively, but Not

"Housekeeping genes" in bacteria are commonly expressed constitutively, but not all of these genes are expressed at the same level (the same number of molecules per cell) . The primary mechanism responsible for variations in the level of constitutive enzymes from different genes is that:

A) all constitutive enzymes are synthesized at the same rate, but are not degraded equally.
B) their promoters have different affinities for RNA polymerase holoenzyme.
C) some constitutively expressed genes are more inducible than others.
D) some constitutively expressed genes are more repressible than others.
E) the same number of mRNA copies are made from each gene but are translated at different rates.