The Lactose Operon, as Well as Other Operons with Genes

The lactose operon, as well as other operons with genes that encode enzymes for the utilization of different carbohydrates, is regulated by the concentration of CRP-cAMP in the cell. One of the consequences is that the cell can have a hierarchy of preferences for the utilization of various carbohydrates. Glucose is at the top of the hierarchy, and when glucose is present in sufficient concentration, the level of CRP-cAMP in the cell is low, and none of the other operons are fully induced even if their associated carbohydrate is present. As the glucose is depleted, the level of CRP-cAMP increases, and each operon in turn becomes fully inducible according to its ranking in the hierarchy. The least preferred carbohydrates require the highest concentration of CRP-cAMP to be fully induced. Suppose the order of preference for sugars were, from most to least preferred after glucose, maltose, lactose, melibiose, trehalose, and raffinose. Which operon would require the highest level of CRP-cAMP to be fully induced?

A) maltose
B) lactose
C) melibiose
D) trehalose
E) raffinose