What is the role of factor XI in the coagulation cascade?

A It activates factor IX
B It activates factor X
C It inhibits thrombin formation
D It activates factor XII
Factor XI is a serine protease that activates factor IX, which then contributes to the formation of thrombin.
Guyton and Hall Textbook of Medical Physiology
Hematology Hematology: Coagulation Disorders Hematology: Coagulation Disorders Hard MEDICAL Confidence: high