Cells of an E. coli strain that are trp lac Z met bio were mixed with cells of an E. coli strain that are trp lac Z met bio and cultured for several hours. Then cells were removed, washed, and transferred to minimal media containing lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How did these few cells become trp lac Z met bio?

A.	transformation.
B.	transduction.
C.	sexduction.
D.	conjugation.
E.	transposition.