What is the average cell cycle duration for a human cell (in $hours$)?

Regarding the sequence of the cell cycle,which one is correct?

The cell cycle remains in a quiescent stage in .........

Mature nerve cells are incapable of cell division. These cells are probably considered to be in:

If a dividing cell is placed in a medium containing radioactive thymidine,the radioactivity will first be observed in:

It is observed that heart cells do not exhibit cell division. Such cells do not divide further and exit $G_{1}$ phase to enter an inactive stage called $G_{0}$ of cell cycle. Fill in the blanks.