An Hfr Strain Has a Plasmid Inserted near the Trp

An Hfr strain has a plasmid inserted near the trp (tryptophan) locus.This Hfr strain is incubated with an F^- trp^- strain.We isolate a trp⁺ strain that can readily donate this trait to other trp^- strains.No other traits are transferred.What has happened?

A) an F⁺ trp plasmid has been generated
B) typical Hfr mating
C) transduction occurs
D) transformation occurs
E) no change in genotype has occurred