Lederberg and Tatum's Landmark Experiment Showed That Gene Transfer Could

Lederberg and Tatum's landmark experiment showed that gene transfer could occur between bacteria,by mixing two strains of bacteria.One strain of bacteria could not synthesize methionine or biotin,but was capable of synthesizing threonine and proline.The other strain was able to synthesize methionine and biotin,but was not capable of synthesizing threonine and proline.Only when these strains were mixed together would they grow on agar that lacked these compounds.What positive control would Lederberg and Tatum have used to ensure that their experiments were accurate?

A) A bacteria that was not cable of synthesizing methionine,biotin,threonin or proline.
B) A bacteria that was capable of synthesizing methionine,biotin,threonin and proline.
C) An agar medium that contained methionine,biotin,threonin and proline.
D) An agar medium that lacked methionine,biotin,threonin,proline,and other nutrients that all bacteria require to grow (e.g.glucose) .
E) No positive control would be used in this experiment because there are already two different strains of bacteria being tested.