Which group of cells would be least likely to contain cells in s phase?

I don't know the given choices but I found an answer to the above question. 

The answer is:
No longer dividing cells of the mammalian brain. Post-mitotic cells will exit the cell cycle and will not contain cells in S phase.

S-phase - part of the cell cycle in which DNA is replicated. Synthesis phase occur between G1 phase and G2 phase.

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