challenge: What is the primary characteristic of Quebec platelet disorder (QPD) that leads to bleeding?
  
  A. Abnormal platelet shape and size
  B. Reduced levels of the fibrinolytic enzyme urokinase-type plasminogen activator (uPA) in platelets
  C. Increased levels of the fibrinolytic enzyme urokinase-type plasminogen activator (uPA) in platelets
  D. Impaired platelet aggregation
  Answer: 