a scientist investigated DNA replication in two groups of cells, labeled A and B. She injected radioactively labled nucleotides into cells of each group and allowed DNA replication to begin. When rerplication was halfway completed, she injected a drug into the cells to stop replication. She then examined the cells to determine the distribution of the newly synthesized DNA. She found each cell of a group A had many segments of new DNA in its nucleus, while each cell of group B had a single segment of new in its cytoplasm.
What can the researcher conclude about the cells ?