Which of the following statements is correct with respect to cell cycle?

Some cells in the adult animals do not appear to exhibit division like the nerve cells. These cells that do not divide further exit G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle. Cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.

The cell in the G1 phase has 2c amount of DNA but at the G2 phase the cell contain 4c amount of DNA as duplication of DNA has already taken place in the S phase. Therefore, G1 phase contain half the amount of DNA as compared to the G2 phase. 

Each chromosome has only 1 chromatid in the G1 phase. During the S phase the amount of DNA doubles, i.e., now there is the formation of another chromatid. These two chromatids are held by the same centromere. Therefore, during the S phase, the amount of DNA doubles but the number of chromosomes remain the same.

DNA content of the cell changes during the cell cycle. During the S phase the amount of DNA doubles.