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: Physiology
Which of the following phase is absent in action potential of pacemaker cells? 
Select and explain. 
A. Phase 0, B. Phase 1, C. Phase 3, D. Phase 4
B: Phase 1
Answer: B: Phase 1 
Explanation: None