A molecular biologist extracts DNA from a lactose positive (Lac ) strain of coli and a penicillin-resistant (PCr) strain of S. aureus. Using restriction enzymes and DNA ligases, she cuts and joins together fragments of the DNA derived from the two organisms, hoping that the lac gene of E. coli will recombine with the PC resistance gene of S. aureus. She uses a process of artificial transformation to insert (transform) the DNA fragments into a strain of E. coli which is penicillin-sensitive (PCs) and lactose negative (Lac-). What medium should she plate the transformants on in order to select for penicillin-resistant, lactose positive recombinant