Which of the following organs is known as the blood bank of the body?

$A$: $A$ portal system consists of veins that start from capillaries and end into capillaries.
$R$: All vertebrates have a hepatic portal system.

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

Select the correct option for myogenic and neurogenic hearts.

Plethysmograph is used to measure

Statement-$I$ :- The body has the ability to alter the stroke volume as well as heart rate and thereby the cardiac output.
Statement-$II$ :- During each cardiac cycle two prominent sounds are produced which can not be easily heard through a stethoscope.