When Lederberg and Tatum performed their experiments on gene transfer in bacteria that lead to our understanding of conjugation,what were their controls?

A)They mixed strains A and B together.
B)They put strain A on one side of a U-shaped tube and strain B on the other,with a filter between them.
C)They found bio^- met^- cells.
D)They plated strain A and strain B separately onto minimal media plates to screen for spontaneous prototrophs.
E)They observed mating bridges with transmission electron microscopes.