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In Escherichia coli, the genes lac , gal , trp , and his are necessary for utilization of lactose, utilization of galactose, synthesis of tryptophan, and synthesis of histidine, respectively, and strs and strr are alleles for streptomycin sensitivity and resistance, respectively. You wish to carry out the cross HFR lac , gal , trp , his , strr X F- lac-, gal-, trp-, his-, strs What medium would you choose to select for gal and to select against strs in a mapping experiment