14. In the Meselson and Stahl experiment, the DNA in the parental generation was all N¹⁵N¹⁵, and after one round of replication, the DNA was all N¹⁵N¹⁴. What DNAs were seen after three rounds of replication, and in what ratio were they found?(A) one N¹⁵N¹⁴, one N¹⁴N¹⁴(B) one N¹⁵N¹⁴, two N¹⁴N¹⁴(C) one N¹⁵N¹⁴, three N¹⁴N¹⁴(D) one N¹⁵N¹⁴, four N¹⁴N¹⁴(E) one N¹⁵N¹⁴, seven N¹⁴N¹⁴