This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
Patients with hemophilia A has bleeding disorder because of- 
Select and explain. 
A. Lack of platelet aggregation, B. Lack of reaction accelerator during activation of factor X in coagulation cascade, C. Neutralization of antithrombin III, D. Release of Thromboxane A2
B: Lack of reaction accelerator during activation of factor X in coagulation cascade
Answer: B: Lack of reaction accelerator during activation of factor X in coagulation cascade 
Explanation: Haemophilia is caused by quantitative reduction of factor VIII in 90% of cases well 10% cases have normal or increased level of factor VIII with reduced activity. factor VIII activates factor X the blood coagulation pathway. But in haemophilia A due to reduced activity of factor VIII ,It can not activate factor X.Therefore , no coagulation exists and increases bleeding. Reference: textbook of Pathology ,7th edition ,author Harsha Mohan, page number 313