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
Which of the following step in cell cycle is known as restriction point? 
Select and explain. 
A. G0 to G1, B. G1 to S, C. S to G2, D. G2 TO M
B: G1 to S
Answer: B: G1 to S 
Explanation: Cells in G1 progress through the cycle and reach a critical stage at the G1/S transition, known as a restriction point, a rate limiting step for replication. Ref: Robbins 8th edition Chapter 3.