This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood Physiology, Subject name: Physiology
[{'content': 'Best index of platelet function is: \nSelect and explain. \nA. Bleeding time, B. Clotting time, C. Clot retraction time, D. Prothrombin time', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bleeding time (N = 1-3 min) is an index of platelet number. Bleeding time is prolonged when platelet number falls below 50,000/mm3. Clot retraction is a function of platelets. The contractile filaments of platelets, in the platelet plug, are responsible for retraction of the clot that has formed on the surface of the platelet plug. Clot retraction occurs by 30-60 minutes after the formation of clot.', 'role': 'assistant'}]