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
Pre-capillary sphincter relaxation is caused by 
Select and explain. 
A. Local metabolites, B. Circulating catecholamines, C. Sympathetic activity, D. Fall in capillary pressure
A: Local metabolites
Answer: A: Local metabolites 
Explanation: Muscle fibers of the capillaries are mostly controlled by the local metabolites as it does not have much sympathetic innervation.