Answer:
Minimal media + glucose + streptomycin
Explanation:
Those capable of synthesizing galactose can grow in minimal media, the availability of streptomycin will destroy those who are susceptible to the antibiotic, whereas glucose, a carbon source from which galactose may be produced and will encourage growth.
Therefore:
The medium should not include galactose when selecting for gal⁺.
Streptomycin should be present in the medium to select against .
The medium to choose is: Minimal media + glucose + streptomycin.