Which of the following is an anticoagulant and prevents blood clotting within the blood vessels?

Which disease can be caused by the $Rh$ factor?

The function of vitamin $K$ is:

The function of the human spleen is to

Which of the following are erythropoietic organs?
$I$. Liver
$II$. Lymph node
$III$. Spleen
$IV$. White bone marrow
$V$. Red bone marrow
Choose the correct option.

$A$ person with an unknown blood group ($ABO$ system) has lost a large amount of blood in an accident and needs an immediate blood transfusion. $A$ friend of the person has a valid certificate of their own blood group and is ready to donate blood without delay. What could be the blood group of the donor friend?