This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
During which phase of the cell cycle the cellular content of DNA is doubled - 
Select and explain. 
A. Mitotic phase, B. G1 phase, C. G2 phase, D. S phase
D: S phase
Answer: D: S phase 
Explanation: There are two resting phases and two active phases in the cycle.
Resting phases → G1 & G2
Active phases


S-phase (synthetic phase) - As the name suggests, synthesis of new DNA takes place, i.e. doubling of DNA occurs.
M-phase (mitotic phase) - Mitosis takes place and the daughter cells receive one copy of DNA. In this phase, cell number is doubled.