The correct answer is d) nucleus.
Replication is the process by which a cell makes a copy of its DNA. In eukaryotic cells, this occurs specifically in the nucleus, where the cell’s genetic material is housed. The nucleus provides a controlled environment for the replication process to take place, ensuring that the DNA is accurately duplicated before the cell divides. In contrast, the cytoplasm is where other cellular processes occur, such as protein synthesis at ribosomes, but DNA replication itself is localized within the nucleus.