The $.....$ is the blood bank of the body.

Select the correct option regarding the clotting of body fluids in a test tube.

Which of the following is an incorrect combination?

Compare the statements $A$ and $B$.
$Statement A$: Blood sugar level falls rapidly after hepatectomy.
$Statement B$: The glycogen of the liver is the principle source of blood sugar.
Select the correct description:

Consider the following four statements regarding the human circulatory system:
$(a)$ Arteries have thick walls and a narrower lumen compared to veins.
$(b)$ Angina is a sudden chest pain.
$(c)$ In the $ABO$ blood grouping system,a person with blood group $AB$ can donate blood to anyone.
$(d)$ Calcium ions play a significant role in blood clotting.
Which two of the above statements are correct?

$A$: In an open circulatory system,the volume of blood is high,but blood pressure is low and irregular.
$R$: In a closed circulatory system,the volume of blood is limited,and blood pressure is high and regular.