Answer:
Semi-conservative
Step-by-step explanation:
Meselson–Stahl experiment proved that DNA replication is a semiconservative process, feeding E. colo bacteria with different types of Nitrogen isotopes (N14 and N15).
Changing the type of radioactive compound in different times of bacteria grow, they could observe that both of the isotopes were present on the bacteria culture.
Basically, if the bacteria present both of them, the DNA was replicated semiconcervely.
Guess what? they show both! (See the image for more information)