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
[{'content': 'Kaolin cephalin clotting time is: \nSelect and explain. \nA. Prothrombin Time, B. Activated paial thromboplastin test, C. Cephalin is a surface activator, D. Kaolin is a platelet phospholipid substitute.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Kaolin cephalin clotting time is the older term to describe activated paial thromboplastin test, which is aimed at detecting the function of intrinsic pathway. In Kaolin cephalin clotting test, kaolin is used as a surface activator, it binds directly to Factor XII resulting in surface activation to XIIa. XIIa cleaves Factor XI to XIa. Cephalin is a phospholipid substitute that replaces platelet phospholipid in the test. Ref: Haematology By Main R. Howard, Peter J. Hamilton, Page 22', 'role': 'assistant'}]