The diagram below shows part of the cell cycle. Normally, checkpoints exist between each phase that monitor whether a cell is ready to move onto the next phase of cell cycle. An error at which of the following checkpoints would be most likely to lead to uncontrolled cell division and cancer?
the checkpoint that prevents cells from leaving M phase until they are ready
the checkpoint that prevents cells from leaving S phase until they are ready
the checkpoint that prevents cells from leaving G1 phase until they are ready
the checkpoint that prevents cells from leaving G2 phase until they are ready