Answer: A. The S-phase.
Explanation: In the S-phase, the replication of DNA occurs, and this is carried out by the DNA polymerase.
During the G-phase, the cell produces new proteins as it continues to grow. At the end of this stage, the cell is assessed to know if it is fit for the next stage -cell division.
The prophase is the first stage of mitosis where the chromatin condenses to form chromosomes.
The metaphase follows immediately, where the condensed chromosomes align themselves before separation. The next stage is the anaphase, and here, the chromosomes separate, and the chromatids move to opposite cell poles.
At the last phase, telophase, the daughter chromosomes travel towards the opposite ends of the nuclear spindles.