question: Q:A 10-year-old boy presents to the emergency department accompanied by his parents with a swollen and painful right knee after he fell from his bicycle a few hours ago. The patient’s mother says he fell off the bike and struck the ground with his whole weight on his right knee. Immediately, his right knee swelled significantly, and he experienced severe pain. The patient’s past medical history is significant for previous episodes of easy bruising that manifest as small bluish spots, but not nearly as severe. The family history is significant for an uncle who had similar symptoms, and who was diagnosed at the age of 13 years old. The patient is afebrile, and the vital signs are within normal limits. On physical examination, a large bruise is present over the right knee that is extending several inches down the leg. The right tibiofemoral joint is warm to the touch and severely tender to palpation. Which of the following is the most likely diagnosis in this patient?? 
  {'A': 'Hemophilia A', 'B': 'Factor V Leiden', 'C': 'Homocystinuria', 'D': 'von Willebrand disease', 'E': 'Protein C deficiency'},