The organ that acts as a filter for blood is:

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?

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

Which of the following figures correctly represents the path of a closed circulatory system?

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

Which organ remains functional for a few hours even after clinical death?