This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Pediatrics
Which plasma protein is necessary for adhesion of platelets to subendothelial fibres? 
Select and explain. 
A. Glycoprotein IIb, B. Von Willebrand factor, C. Platelet factor 3, D. Factor X
B: Von Willebrand factor
Answer: B: Von Willebrand factor 
Explanation: b. Von Willebrand factor(Ref: Nelson's 20/e p 2386-2390, Ghai 8/e p 349)Von Willebrand factor present in plasma and expressed on endothelium after tissue injury is necessary for platelet adhesion with the help of Gp Ib/IX on platelets.