Which of the following formed elements activates the plasma clotting factors?

Which type of white blood cells are concerned with the release of histamine and the natural anticoagulant heparin?

With regard to the $ABO$ blood typing system,if a man who has type $B$ blood and a woman who has type $O$ blood were to have children,what blood types could the children have?

Which of the following ions is essential for the synthesis of hemoglobin?

What is the first site of hematopoiesis in a human embryo?

Which one of the following blood groups belongs to the category of universal recipient?