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

Given below are four statements $(i-iv)$ regarding the human blood circulatory system.
$(i)$ Arteries are thick-walled and have a narrow lumen as compared to veins.
$(ii)$ Angina is acute chest pain when the blood circulation to the heart muscle is reduced.
$(iii)$ Persons with blood group $AB$ can donate blood to any person with any blood group under the $ABO$ system.
$(iv)$ Calcium ions play a very important role in blood clotting.
Which two of the above statements are correct?

Analogy type questions:
$(1)$ Fish : Single circulation :: Amphibians : ...........
$(2)$ Between right atrium and right ventricle : Tricuspid valve :: Between left atrium and left ventricle : .............

Which of the following flowcharts correctly represents the process of blood clotting?

Which of the following is $NOT$ a character of open circulation?

$A$: Elevated levels of $Na^+$ decrease the heart rate and contractility.
$R$: Elevated $Na^+$ levels increase the excitability of the $SA$ node.