The answer is B: G2 checkpoint.
Cell cycle checkpoints are control mechanisms necessary for proper cell division. In the cell cycle, there are two checkpoints: the G1 checkpoint and the G2 checkpoint. The G1 checkpoint is right before the S phase, and G2 checkpoint is right before the M phase.
The G2 checkpoint is a DNA damage checkpoint and if DNA is damaged, entering the cell cycle is delayed before mitosis (M phase).