This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood: Hemostasis and Blood Coagulation, Subject name: Physiology
Factor which activates preaccelerin to Vila - 
Select and explain. 
A. Tissue factor, B. Christmas factor, C. Fibrim, D. Prothrombin
A: Tissue factor
Answer: A: Tissue factor 
Explanation: Ans. is 'a' i.e., Tissue factor o Preaccelerin (factor VII) is activated to factor Vila by tissue factoro Tissue factor is the cofactor for both factor VII and Vilao When IF binds to factor VII it promotes its activation to Vilao When TF binds to Vila, the TF- Vila complex catalyzes the activation of factor X.