Which of the following plasma proteins is involved in the coagulation of blood?

Blood is formed of

Megakaryocyte cells are .....

A child of a mother with blood group $A$ and a father with blood group $AB$ may have any one of the following blood groups except

What are blood platelets a source of?

$A$ person injured in a road accident does not have a known blood group and requires an immediate blood transfusion. $A$ doctor friend offers to donate blood immediately. What would be the blood group of this doctor?