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: Biochemistry
Which parts of cell cycle are fixed in durationa) GIb) G2c) Sd) M 
Select and explain. 
A. c, B. d, C. bcd, D. ac
C: bcd
Answer: C: bcd 
Explanation: The time taken for S, G2 and M phases are similar for most cell types, occupying about 6, 4 and 2 hours respectively whereas the duration of G1 shows considerable variation as short as 2 hours in rapidly dividing cells i.e., embryonic tissue or longer than 12 hours in some adult tissue.