Answer:
The correct answer would be A) S.
S or synthesis phase is the phase of cell cycle in which the replication of DNA takes place.
It takes place between G1 and G2 phases of the cell cycle.
The concentration of DNA becomes twice after completion of the S phase. However, the number of chromosomes remain the same.
Each chromosome produces the sister chromatid after this phase which are divide equally in daughter cells after M phase.