E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What...

E. coli cells grown on 15N medium are transferred to 14N medium
and allowed to grow for two more generations (two rounds of
DNA replication). DNA extracted from these cells is centrifuged.
What density distribution of DNA would you expect in this
experiment?
(A) one high-density and one low-density band
(B) one intermediate-density band
(C) one high-density and one intermediate-density band
(D) one low-density and one intermediate-density band