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
Pacemaker potential occurs due to 
Select and explain. 
A. Opening of transient, rapid T-type Ca2+ channel, B. Opening of K+ channel, C. Closure of Ca2+ channel, D. Closure of funny Na+  channel
A: Opening of transient, rapid T-type Ca2+ channel
Answer: A: Opening of transient, rapid T-type Ca2+ channel 
Explanation: Pacemaker potential occurs due to

Opening of slow type funny Na+ channel
Opening of transient, rapid T-type Ca2+ channel
Early closure of K+ channel