Select the correct option for myogenic and neurogenic hearts.

The $pH$ of blood in an artery and a vein is:

$A$: 'Dub' is a long and sharp sound.
$R$: It is caused by the closing of atrioventricular valves.

The breakdown product of haemoglobin is

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?

Differentiate between closed circulatory system and open circulatory system.