Describe how you would identify E. coli mutants that cannot utilize galactose as a carbon (energy) source. You are given a test tube containing E. coli grown under full nutrition, a spreader, filter paper, Petri plates with agar gel containing various nutrients, and an incubator. There are two kinds of Petri plates provided: agar gel was made with either inorganic salt + glucose [plate A], or inorganic salt + galactose [plate B].