Answer: S phase
Step-by-step explanation:
S phase occurs during interphase, which is the process in cell cycle in which DNA is created and replicated. Once a cell enter S phase, it is almost guaranteed to enter mitosis or meiosis because the DNA is doubled in order to then be split in daughter cells. If a cell were not to enter S phase, there would not be enough DNA to split it during mitosis and meiosis, meaning the process would most likely simply not happen.