Answer:
Murine, primate and human embryonic stem cells (ESCs) exhibit a very unusual cell cycle structure, characterized by a short G1 phase and a high proportion of cells in the S-phase.
Explanation:
Normally, embryonic stem (ES) cells proliferate quickly during differentiation and do not differentiate simply by cell cycle slowing. In this paper, it is shown that the role of the cell cycle in terminal stages of differentiation can be adapted for and extended into ES cells.
I would go with hypothesis because I never heard any of the other answers in Bio and a hypothesis is an educated guess so it means what you already know and it’s an observation (I hope this helped!!)