Regarding the Cell Cycle, Which, If Any, of the Following

Regarding the cell cycle, which, if any, of the following statements is correct?

A) The M phase and the S phase are the critically important phases of the cell cycle; according to circumstance, the G₂ phase and the G₁ phase are dispensable.
B) The M phase is the only phase in the cell cycle when chromosomes stained with chemical dyes are visible under the light microscope.
C) The G₀ phase is a specialized phase that allows terminally differentiated cells to irretrievably exit the cell cycle and become post-mitotic cells.
D) The G₀ phase is a modified version of the G₂ phase.