Why Is It a Good Idea for a Bacterial Cell

Why is it a good idea for a bacterial cell to be able to utilize glucose FIRST as an energy source (until it's used up) ,THEN switch to lactose?

A) Glucose is an easier compound to break down and obtain energy from than lactose.
B) Lactose cannot be used by bacterial cells as an energy source.
C) It's about conservation of energy-why expend the energy to make the extra enzymes for breaking down lactose when glucose is right there and doesn't need the extra enzymes for breakdown.
D) Glucose provides 10x as much energy when broken down as lactose.
E) Glucose is no easier compound to break down and obtain energy from than lactose AND It's about conservation of energy-why expend the energy to make the extra enzymes for breaking down lactose when glucose is right there and doesn't need the extra enzymes for breakdown.