Matthew Meselson and Franklin Stahl demonstrated that DNA replication is semiconservative in bacteria. Choose the correct description of their experiment. A. Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication. B. Meselson and Stahl initially cultured E. coli in medium containing both 14N and 15N until all cells contained only 14N/15N DNA. They then cultured the 14N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication. C. Meselson and Stahl initially cultured E. coli in medium containing both 14N and 15N until all cells contained only 14N/15N DNA. They then cultured the 14N/15N E. coli in medium containing only heavy nitrogen (15N) and collected samples after one, two, and three rounds of DNA replication. D. Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in medium containing both 14N and 15N and collected samples after one, two, and three rounds of DNA replication.