The answer is a. contain checkpoints that determine if the cycle will continue. Cell cycle checkpoint are important mechanisms that control cell division. There are two checkpoints during the cell cycle: G1 and G2 checkpoint. The G1 checkpoint is right before the S phase. If something is wrong at the G1 checkpoint, the cell will not enter the S phase where DNA replication starts. The G2 checkpoint (DNA damage checkpoint) is right before the M phase. If DNA is damaged, the cell will not enter the M phase (mitosis).
