The is critical in the cell cycle because it indicates the cell is ready for division. g0 phase g1 phase g2 phase s phase.

The correct answer is S phase.

The critical phase of cell cycle is S phase, in this phase the DNA starts replicating.The cell cycle is called the synthesis phase because the synthesis of DNA starts in this phase. There is no chance that the cell can go back to the previous phase. The DNA within the cell starts replicating. Depending upon the level of nutrients, energy and external factors, cells must decide that they will enter into cell cycle or not.